National Academies Press: OpenBook

Design of Construction Work Zones on High-Speed Highways (2007)

Chapter: Chapter 3 Current Work Zone Design Guidance

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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Suggested Citation:"Chapter 3 Current Work Zone Design Guidance." National Academies of Sciences, Engineering, and Medicine. 2007. Design of Construction Work Zones on High-Speed Highways. Washington, DC: The National Academies Press. doi: 10.17226/14032.
×
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Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 18 CHAPTER 3 CURRENT WORK ZONE DESIGN GUIDANCE This chapter includes a review of current guidance related to construction work zone design. The reviewed references include the 2003 MUTCD (4), 2001 Policy on Geometric Design of Highways and Streets (Green Book) (5), 2002 Roadside Design Guide (6), 2000 Highway Capacity Manual (27), and the design guidance of state DOTs. (Because most readers will be familiar with the national manuals, reference notes will not be inserted at subsequent referrals to them in this report.) The DOT guidance was obtained through a search of Web-accessible guidance during the review of work zone research and through a survey of state DOTs conducted under this project. 3.1 NATIONAL GUIDANCE Although nationally recognized design and analysis methods have been developed for many highway engineering disciplines (e.g., bridge, geometry, pavements), similar guidance for the design of work zones on high-speed highways does not exist. Several national publications provide useful guidance; however, a comprehensive process for the design and analysis of work zones has not been developed. The following review outlines the current guidance in these documents, as well as gaps in national guidance related to the design of construction work zones on high-speed highways. 3.1.1 Manual on Uniform Traffic Control Devices The MUTCD is an authoritative publication with nationwide applicability. It provides information on traffic signals, signs, pavement markings and numerous other devices. Part 6 of the MUTCD focuses on temporary traffic control, and portions of it are directly applicable to stationary work zones on high-speed highways (e.g., lane reduction tapers). Part 6 also addresses a wide variety of topics that are not directly related to the scope of this research report, including mobile and short-term, stationary work zones. By definition, the MUTCD pertains to traffic control devices; therefore, Part 6 provides extensive guidance on the application of specific devices (e.g., drums, barricades and signs) to work zones. Its intended purpose is to “depict common applications of temporary traffic control devices” that “provide for the safe and efficient movement of vehicles, bicyclists, and pedestrians through or around temporary traffic control zones while reasonably protecting workers and equipment.” Although traffic control devices are an important element, they are but a part of work zone design. As indicated by the following excerpt, Part 6 provides limited guidance in some aspects of work zone design: “The basic safety principles governing the design of permanent roadways should also govern the design of temporary traffic control zones. The goal should be to route road users through such zones using roadway geometrics and roadside features and temporary traffic control devices as nearly as possible to normal highway situations” (emphasis added).

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 19 This passage, in effect, recommends that work zones be designed to approximate the geometric and roadside criteria applicable to permanent facilities. Although the MUTCD does not refer to a source for these criteria, the Green Book and Roadside Design Guide (reviewed below) are the logical references for information on normal roadway geometrics and roadside features. The Green Book is the pre-eminent guidance document for geometric design. It outlines fundamental design conventions and principles and provides horizontal and vertical alignment and cross section criteria for all facility types. Green Book criteria are generally applied to the permanent features of new construction and reconstruction projects. Given the temporary nature and physical constraints inherent in construction areas, using permanent roadway geometric criteria as a goal is unwarranted and impractical. The MUTCD divides the typical temporary traffic control zone into four areas: the advance warning area, the transition area, the activity area, and the termination area. Many of the studies on work zone crashes have adopted these classifications. The advance warning area is the section of highway where road users are informed about the upcoming work zone. For stationary construction, it usually consists of a series of signs. The transition area is the section of highway where road users are directed out of their normal path to a new path. This usually involves the strategic use of tapers. The activity area is the section of the highway where the work activity takes place. It is comprised of the work space, the traffic space (i.e., the area of highway in which the road users are routed through the activity area), and the buffer space (the lateral or longitudinal area that separates road user flow from the work space or an unsafe area). Finally, the termination area is where the road users are returned to their normal path. Other guidance given in Part 6 of the MUTCD that will have an effect on work zone design elements other than traffic control devices relates to: • Reduced speed limits - “Reduced speed limits should be used only in the specific portion of the temporary traffic control zone where conditions or restrictive features are present. However, frequent changes in speed limit should be avoided. A temporary traffic control plan should be designed so that vehicles can safely travel through the temporary traffic control zone with a speed limit reduction of no more than 10 mph. . . . . Where restrictive features justify a speed reduction of more than 10 mph. . . the speed limit should be stepped down in advance of the location requiring the lowest speed. . . . Reduced speed zoning [lowering the regulatory speed limit] should be avoided as much as practical because drivers will reduce their speeds only if they clearly perceive a need to do so.” • Tapers - The types of and criteria for tapers are given in Tables 6C-3 and 6C-4 of Part 6 of the MUTCD [see Figure 1]. Tapers are created by using a series of channelizing devices and/or pavement markings to move traffic out of or into the normal path. Tapers are used in the transition and termination areas.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 20 Table 6C-3. Taper Length Criteria for Temporary Traffic Control Zones Type of Taper Taper Length (L)* Merging Taper at least L Shifting Taper at least 0.5L Shoulder Taper at least 0.33L One-Lane, Two-Way Traffic Taper 100 ft maximum Downstream Taper 100 ft per lane Table 6C-4. Formulas for Determining Taper Lengths Speed Limit (S) Taper Length (L) Feet 40 mph or less 60 WSL 2 = 45 mph or more WSL = Where: L = taper length in feet W = width of offset in feet S = posted speed limit, or off-peak 85th-percentile speed prior to work starting, or the anticipated operating speed in mph Figure 1. Tables 6C-3 and 6C-4 from the 2003 MUTCD. • Traffic barriers - Traffic barriers should be used to protect workers. The barriers should be placed along the work space, depending on factors such as lateral clearance of workers from traffic, traffic speed, duration and type of operations, time of day, and volume of traffic. It is recommended that Chapter 9 of the Roadside Design Guide be used for barrier design and placement. In summary, the MUTCD provides extensive information on the design and application of traffic control devices used in temporary traffic control zones, as well as typical traffic control zone set-ups based on duration, location, type of work, and highway type. The only information given that relates (directly or indirectly) to geometric design elements (i.e., cross section, horizontal alignment, etc.) deals with speed limit reduction and taper design. For the elements outside the scope of the MUTCD, it is recommended that the roadway geometrics and roadside features compare as nearly as possible to normal highway situations.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 21 3.1.2 A Policy on Geometric Design of Highways and Streets The 2004 Green Book provides geometric design guidance for permanent roads. Work zones are addressed briefly in the Green Book’s Chapter 3 under the section, Maintenance of Traffic through Construction Areas, and the guidance is limited to three pages. Where “traffic lanes are closed, shifted, or encroached upon in order that the construction be undertaken” the Green Book recommends that a traffic control plan should be developed to “minimize the effect on traffic operations by minimizing the frequency or duration of interference with normal traffic flow.” It advises that “a well thought out and carefully developed plan for the movement of traffic through a work zone will contribute significantly to the safe and efficient movement of traffic as well as the safety of the construction forces.” It also suggests that the traffic control plan have some built-in flexibility for unforeseen changes in work schedules, delays and traffic patterns. The traffic control plan includes the layout of the construction area as well as the use and application of signs and other traffic control devices. The Green Book references the MUTCD for guidance in the selection of traffic control devices and stresses the importance of its use. The Green Book also gives the following very minimal guidance with respect to the roadway geometry through the construction area: • The traffic control plan should use geometrics and traffic control devices as nearly comparable to those for normal operating situations as practical, while providing room for the contractor to work effectively; • A clear zone should be provided between the work space and the passing traffic and under certain conditions, a positive barrier is justified; • Adequate tapers should be provided for lane drops or where traffic is shifted laterally. Other guidance relating to geometric issues, pavement, and traffic control include 1) increasing the capacity when using an existing road as a detour by eliminating troublesome turning movements and physically widening the travel way; 2) providing adequate delineation and warnings for geometric features and roadway environments on detours and temporary connections that require more guidance and alertness; 3) maintaining the surface of the traveled way so that it is in a condition to permit the safe movement of traffic at reasonable speeds; and 4) providing for all pedestrian flows. No dimensional guidance or quantitative methods are included. 3.1.3 Roadside Design Guide The 2002 Roadside Design Guide devotes Chapter 9 to Traffic Barriers, Traffic Control Devices, and Other Safety Features for Work Zones. The chapter is intended to be used in conjunction with Part 6 of the MUTCD by adapting the criteria from Roadside Design Guide Chapters 1 through 8 and, where warranted, applying them to work zones. The chapter states, “The design and selection of work zone safety features should be based on expected operating speeds and proximity of vehicles to workers and pedestrians.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 22 Actual operating speeds may be considerably higher than posted speed limits and as much as 20 to 25 mph faster on freeways when temporary 40 mph zones are established.” The clear zone is a key element of roadside design for permanent roadways. Chapter 9 provides the following guidance on the application of the clear zone concept to work zones (paraphrased and quoted): The forgiving roadside concept should be applied to all work zones as appropriate for the type of work being done and to the extent that existing roadside conditions allow. This includes providing a clear recovery area for longer term projects and using traffic control devices and safety appurtenances that are crashworthy or shielded. The work zone clear zone is defined as “the unobstructed relatively flat area impacted by construction that extends outward from the edge of the traveled way.” Because of the limited horizontal clearance and heightened awareness of drivers in work zones, the clear zone requirements are less, and “engineering judgment” must be used in applying the clear zone concept to work zones. Some designers determine clear zone widths on a project-by-project basis (based on speeds, geometrics, etc.) whereas others use a specified width. Where available, the widths of commonly used work zone clear zones are 12 to 18 feet, with collateral hazards such as equipment and stored materials calling for widths greater than 30 feet from the traveled way. The tabulated clear zone widths used by one (unspecified) state are provided as an example (reproduced from Chapter 9 as Figure 2). TABLE 9.1 Example of clear zone widths for work zones Speed [mph] Widths [ft] [60-70] [30] [55] [23] [45-50] [16] [30-40] [13] Figure 2. Table 9.1 of the 2002 Roadside Design Guide. The Chapter 9 guidance on work zone clear zones appears to be a summary of current practice (“commonly used work zone clear zones are. . .”). The guidance also imparts flexibility and discretion in dealing with construction work zones (“to the extent that existing roadside conditions allow”) (“where width is available”).

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 23 Other Roadside Design Guide Chapter 9 guidance addresses: • Providing a safe environment for pedestrians, bicyclists, and highway workers - which may include providing safe pathways where pedestrians and bicyclists are allowed to traverse the work zone by shielding adjacent excavations or other unsafe areas; • Use of temporary or permanent traffic barriers - to protect traffic from entering work areas such as excavations or material storage sites, provide positive protection for workers, separate two-way traffic, protect construction such as falsework for bridges and other exposed objects, and separate pedestrians from vehicular traffic. Chapter 9 covers the physical properties (e.g., dimensions, weight, deflection, etc.) and mechanical installation (e.g., connections) of barriers. Some of the Chapter 9 barrier use guidance is quantitative, while other advice is primarily qualitative in nature. Examples are provided below (paraphrased): • Use of temporary longitudinal barriers should be based on an engineering analysis; • The portable, concrete, safety-shape barrier (PCB) is the option preferred by most state transportation agencies; • No consensus on specific barrier warrants exists. Barriers are usually justified for bridge widening, shielding of roadside structures, roadway widening (especially with edge drop-offs), and separating two-lane, two-way traffic on one roadway of a normally divided facility; • A minimum offset of 2 feet from the travel lane of a PCB is desirable; • Benefit-cost analyses indicate that accident costs are minimized for flare rates of 4:1 to 8:1. A flare rate of 5:1 or 6:1 may be favorable for urban streets with higher volumes, lower speeds, and higher impact angles; • In situations of restricted geometry (e.g., intersecting roadways near or within the work activity area) where expected impacts could be greater than 25 degrees, the designer should refer to NCHRP Report 358, Traffic Barriers and Control Treatments for Restricted Work Zones; • Desirable end treatments and acceptable (for low speeds) end treatments are given in section 9.2.2; • Adequate transitions should be made between temporary barriers of differing flexibility or between temporary and permanent barriers. Several types of stationary and temporary crash cushions and their properties are identified in Chapter 9. Temporary crash cushions include truck mounted attenuators (TMAs). These TMAs may be used for moving operations or at long-term, stationary construction sites. Their suggested uses are given in Table 9.3 of the Roadside Design Guide (Figure 3). Quantitative guidelines for the recommended buffer distances and spacing of these vehicles are also given.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 24 The Roadside Design Guide Chapter 9 also contains information regarding the dimensions, crashworthiness, use and placement of traffic control devices for work zones. These include channelizing devices (e.g., cones and tubular markers, vertical panels, drums, barricades) and signs and supports. Traffic control devices should be designed and installed such that impact severity is minimized. In the Roadside Design Guide, work zone traffic control devices are grouped into four categories based on their crashworthiness (i.e., their relative safety when struck by a vehicle). These categories were first established in one of two FHWA memoranda on guidance for crash testing of work zone traffic control devices (28): • Category I devices were those lightweight devices that could be self-certified by the vendor; • Category II devices were other lightweight devices that needed individual crash testing; • Category III devices were barriers and other fixed or massive devices also needing crash testing; • Category IV devices were trailer-mounted lighted signs, arrow panels, etc. The second memorandum listed devices that were acceptable under Categories I, II, and III (29). Some final guidance in Roadside Design Guide Chapter 9 addresses: • Use of glare screens to reduce headlight glare and block the view of work zone activities that may distract the driver (here qualitative guidance is given on considerations when deciding whether to install glare screens); • Avoiding large (greater than 2 inches) pavement edge drop-offs and providing mitigation depending on the extent of the drop-off. In summary, the Roadside Design Guide contains significant information on the physical characteristics and crashworthiness of work zone traffic control devices and barriers. However, guidance is limited with respect to specific dimensions (i.e., clear zone width, slopes, horizontal clearance) and barrier placement guidance. 3.1.4 Highway Capacity Manual The 2000 Highway Capacity Manual Chapter 22 contains guidance on how to investigate reduced capacity resulting from construction and maintenance freeway work zones. This guidance is important in that decisions about lane widths, the number of travel lanes, etc. that agencies will allow during construction are typically based on considerations of whether traffic volumes expected to use the work zone can be adequately accommodated through the work zone. The Highway Capacity Manual divides construction activities into short-term and long-term; however, its definitions differ from those used for this research. The Highway Capacity Manual suggests that the primary distinction between short-term and long-term work zones is the type of devices used to demarcate the work area, with long-term using portable concrete barriers and short-term using conventional channelizing devices (traffic cones, drums, etc.).

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 25 Table 9.3 Suggested priorities for application of protective vehicles and truck mounted attenuators Ranking* Non-Freeway Closure/Exposure Condition Examples of Typical Construction Maintenance Activities Freeway 50 mph 45 mph 40 mph Mobile Activities: No Formal Lane Closure Shadow vehicle for operation Crack pouring, patching, A-1 A-2 A-3 A-4 involving exposed personnel utility work, striping, coning Shadow vehicle for Sweeping, chemical E-1 E-2 E-3 E-4 operation not involving spraying exposed personnel No Formal Shoulder Closure Shadow vehicle for operation Pavement repair, pavement B-2 B-3 C-3 C-3 involving exposed personnel marking, delineator repair Barrier vehicle for operation Open excavation, E-2 E-3 E-4 E-5 not involving exposed temporarily exposed bridge personnel pier Stationary Activities: Formal Lane Closure Barrier vehicle for operation Pavement repair, pavement B-2 B-3 C-4 D-5 involving exposed personnel marking Barrier vehicle for condition Open excavation E-2 E-3 E-4 E-5 involving significant obstruction Formal Shoulder Closure Barrier vehicle for operation Pavement repair, pavement C-3 C-4 D-5 D-5 involving exposed personnel marking, guardrail repair Barrier vehicle for condition Open excavation E-3 E-4 E-5 E-5 involving significant obstruction *The alphabetic ranking indicates the priority assigned to the use of a protective vehicle. The use of protective vehicles: A – is very highly recommended E – may be justified on the basis of special conditions encountered B – is highly recommended on an individual project when an evaluation of the circumstances C – is recommended indicates that an impact with a protective vehicle is likely to D – is desirable result in less serious damage and injury than would impact with a working vehicle or the obstruction *The numerical rank indicates the level of priority assigned to the used of a TMA on an assigned protective vehicle. The use of a TMA under the defined conditions: 1 – is very highly recommended 4 – is desirable 2 – is highly recommended 5 – may be justified on the basis of special conditions encountered 3 – is recommended on an individual project Figure 3. Table 9.3 of the 2002 Roadside Design Guide.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 26 A methodology for calculating the capacity of short-term freeway work zones has been developed (30). The capacity is given by NfRIc HVa **)1600( −+= (1) Where =ac adjusted mainline capacity (vehicles per hour); =1600 the “base” capacity for short-term freeway work zones; =I adjustment factor for the intensity of work activity, referring to the numbers of workers on site, the number and size of work vehicles in use, and the proximity of the work to the travel lanes; the values for I range from -160 to +160 passenger cars per hour per lane (pc/hr/l) and “should be applied on the basis of personal judgment, recognizing that 1,600 pc/hr/l is an average over a variety of conditions”; =R adjustment factor for ramps resulting from the following Highway Capacity Manual narrative: entrance ramps should be located at least 1,500 feet upstream from the beginning of the full lane closure; if that cannot be done, then either the ramp volume should be added to the mainline volume, or the capacity of the work zone should be decreased by the ramp volume (up to half the capacity of one lane, assuming that at very high volumes mainline and ramp volumes will alternate); =HVf the same heavy vehicle adjustment factor used elsewhere in the manual, here used to account for the effects of heavy vehicles in the work zone; =N number of lanes open through the short-term work zone. ( )11 1 −+ = TT HV EP f (2) Where =TP proportion of heavy vehicles; =TE passenger car equivalent for heavy vehicles. For long-term construction work zones, the capacity values are based on research in (31) and shown in table 6.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 27 Table 6 Summary of capacity values for long-term construction zones (32) Number of Normal Lanes Lanes Open Number of Studies Range of Values (Vehicle/Hr/Lane) Average Values (Vehicle/Hr/Lane) 3 2 7 1,780-2,060 1,860 2 1 3 — 1,550 The Highway Capacity Manual also gives the following research-based (30,31) guidance: “If traffic crosses over to lanes that are normally used by the opposite direction of travel, the capacity is close to the 1,550 vehicles/hour/lane value. . . . If no crossover is needed, but only a merge down to a single lane, the value is typically higher and may average about 1,750 vehicles/hour/lane.” Finally, based on another research study (32), capacity reductions as a result of reductions of lane width in freeway work zones are given. “For traffic with passenger cars only, headways increase by about 10 percent in going from 11-foot widths to 10.5- or 10-foot widths and by an additional 6 percent in going to 9-foot widths.” These translate into 9 and 14 percent drops in capacity, respectively. 3.1.5 Summary In summary, the MUTCD, Green Book, and Roadside Design Guide, which are frequently referenced by highway engineers, provide guidance on work zones but leave substantial voids related to geometrics, relationships among geometrics and appropriate traffic control, roadside design, and special features used exclusively or primarily in construction work zones. The underlying principles across all three documents are, for work zone elements that fall outside the realm of their guidance: “(use) the basic safety principles governing the design of permanent roadways. . .” and “route road users through such zones using roadway geometrics, roadside features and TTC (temporary traffic control) devices as nearly as possible comparable to those for normal highway situations” (from MUTCD). This advice, although perhaps desirable, is limited and impractical. In addition, guidance presented in the Highway Capacity Manual on determining capacity reductions as a result of construction or maintenance freeway work zones is quite limited. FHWA recognized the benefits of greater standardization when it established the National Highway Work Zone Safety Program by stating, “Having appropriate national and state standards and guidelines would contribute to improved safety” (35). With national guidelines as a base, individual DOTs can adopt or adapt them to meet the unique needs and conditions of their jurisdictions.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 28 3.2 STATE TRANSPORTATION AGENCY GUIDANCE AND PRACTICE The primary objective of this research is to develop a comprehensive design- decision methodology that, when properly applied, will result in the safe and efficient movement of traffic through construction work zones on high-speed highways. Therefore, a review of current work zone design guidance from state transportation agencies was conducted. A significant amount of information was identified and reviewed regarding how state DOTs design work zones. As with other information sources on this topic, state DOT publications on work zones usually address the full array of categories (e.g., low- speed/high-speed, short-term/intermediate-term/long-term, mobile/stationary), not just construction work zones on high-speed highways. Information included in this summary was obtained from two sources: • State DOT survey conducted during the research - States were asked to respond to specific questions and to provide their policy and guidance publications. In many cases the applicable state documents were Web-based, in which case the states provided URLs. Thirty-two states returned survey questionnaires. After the responses were reviewed, ten states were contacted for clarification and supplemental information. This generally resulted in useful information being included in the summary. In a few cases, the original response was not useful. In those instances where the DOT response did not yield reasonable or relevant interpretation, the original response was not reported. For example, one DOT’s responses consistently referred to their practice for “non construction” work zones. The research team received no response to follow-up requests for information regarding construction work zones and therefore the information will not be included in the review. • Review of state DOT Web-accessible information - Every state DOT has a Web site. To varying degrees, these sites provide access to policies, criteria, and procedures. A search of these sites was conducted. Much of the material retrieved through the Web search duplicated that obtained through the survey. However, additional useful information was also found. Mostly, this consisted of information from the Web sites of state DOTs that did not return a completed questionnaire. In several cases, the information provided by a completed questionnaire was augmented by a search of the responding agency’s Web site. Work zone design processes have been developed and documented to a fairly extensive degree within state DOTs. Of the 32 states responding to the survey questionnaire, 25 (78 percent) indicated having a publication that provides policy or guidance on the design of work zones and traffic control plans. However, in some cases the documents or publications were not made available. The breadth and depth of guidance varies widely among states. In some cases, temporary traffic control is the primary or exclusive area of guidance, while other states

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 29 address traffic management strategies, geometric design, drainage, roadside safety and traffic barriers, and interchange auxiliary lanes, in addition to traffic control. The construction work zone design information of some states is distributed among traffic control and design guidance and standard drawings. Several state DOTs have a document that is similar in scope to the Part 6 of the MUTCD. In some cases, topic-specific memoranda or reports were provided as the source of guidance. Three states submitted draft and interim guidance documents on a specific topic (e.g., use of temporary barriers). In narrative responses, several states also indicated an intention to revisit or revise a particular aspect of their current practice. Overall, the collected information enabled development of a fairly comprehensive summary of state DOT construction work zone design practice for high-speed highways. While there are differences in the manner construction work zones and permanent roads are designed, there are also many process similarities. The ensuing paragraphs summarize what was learned about state DOT work zone design practices on a variety of topics. 3.2.1 Work Zone Design Strategies and Assessment Several state DOTs have guidance on conceptual work zone design. The information from DOTs in California, Connecticut, and Indiana was found to be the most comprehensive. Information from the latter two is very similar, and information from all three shares common elements. These three DOTs also provide guidance related to development of traffic operations plans (e.g., supplemental transit, corridor capacity strategies), which is very useful but is separate from a traffic control plan and therefore not reported here. To varying degrees, DOTs with less comprehensive guidance publications also address some of the topics covered below. The following work zone types are identified and characterized in the guidance documents reviewed: • Alternating one-way operation (one-lane, two-way operation); • Crossover; • Detour; • Diversion (runaround); • Lane constriction; • Lane closure; • Intermittent closure; • Use of shoulder or median. These work zone types are presented as options, or the menu from which a selection(s) is made. 3.2.1.1 Capacity Considerations The capacity through construction work zones is typically less than prior to the project. No information was found in state DOT publications on methods to quantitatively determine the effect of construction work zones on capacity. However, Illinois DOT provides qualitative guidance on options to mitigate capacity reductions associated with construction work zones (e.g., temporary parking restrictions, contra-flow lanes). Several

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 30 computer software packages have the capability to assess work zone traffic operations but no references to these tools were found in the DOT work zone design guides. 3.2.1.2 Construction Contract Options Illinois DOT’s work zone design guidance identifies several common construction strategies (e.g., reconstruction by halves, serial/segmental reconstruction) and phasing options. The advantages and disadvantages of each are discussed. Additionally, A+B bidding (also known as A+Bx) and incentive/disincentive contract options are identified and discussed. 3.2.1.3 Strategy/Type Selection Several DOTs provide the same or a similar chart for use in identifying feasible work zone types for various facility characteristics (e.g., number of lanes, traffic) and construction activity. The chart from Connecticut DOT’s guidance is included as Figure 4. 3.2.2 Principles of Design Maintaining traffic through a construction work zone often requires providing a road on a location different from the permanent road for which it substitutes. This necessitates a series of design decisions similar to those associated with permanent roads. The temporary nature of work zones is a defining characteristic and one that distinguishes them from permanent roads. The attribute of limited service life is implicit to many decisions and explicitly reflected in several state DOT publications. The temporary nature of work zone roads and some roadside features are identified as a consideration in establishing criteria and as guidance for decision processes. Consequently, several state DOTs do not apply the same design criteria to a work zone road or roadside as are applied to permanent facilities. These variations are found in various design criteria and decision processes of state DOTs. 3.2.2.1 Speed Speed and its relationship to design decisions is a complex subject for permanent roads. The relationships among design speed, regulatory speed, and operating speed are not consistent. An ongoing research project (NCHRP Project 15-25) was initiated to study these issues and evaluate alternatives to the design speed approach used for permanent roads. The situation for work zones can be further complicated when it is desirable to reduce speed at the work zone in relation to that of the approaching road and pre-project conditions. Further, there is a perception that lower speeds within work zones will improve safety, and considerable effort is often expended to induce speed reductions.

F inal R eport for N C H R P R eport 581: D esign of C onstruction W ork Z ones on H igh-S peed H ighw ays C opyright N ational A cadem y of S ciences. A ll rights reserved. CONSTRAINTS LANE CONSTRICTION (Use part of the shoulder if Restripe lane lines; keep lanes 3.0 m or wider. For freeways and other divided highways, the minimum lane width is 3.3 LANE CLOSURE ONE-LANE, TWO-WAY OPERATION TEMPORARY ROADWAY Sufficient right-of-way INTERMITTENT CLOSURE Off-peak hours USE OF SHOULDER/MEDIAN (As a full lane) May need to upgrade shoulder CROSSOVER TWO-WAY TRAFFIC ON DIVIDED FACILITIES DETOUR TO EXISTING ROAD Reasonable detour route(s) available. Maintain local Feasible CHART FOR IDENTIFICATION OF FEASIBLE WORK ZONE TYPES 1 meter (m) = 3.28 feet. Figure 4. Sample work zone type feasibility chart (Connecticut DOT) Data Base Location of Work Work Procedure Tentative Schedule Traffic Volume Work Requires Closure Both Directions? A lte rn at e W or k Zo ne T yp es 2-Lane Road With Shoulder 2-Lane Road Without Shoulder Multi-Lane Arterial Street Without Shoulder Freeway Shoulder Paved and 2.4 m or Wider? Work Requires Closure Both Directions? Work Requires Closure of All Lanes in One Direction? Work Requires Closure of All Lanes in One Direction? Work Requires Closure of One or More Full Lanes? Paved Shoulder 2.4 m or Wider? NO NO NO NO NO YES NO YES YES YES YES NO YES YES

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 32 Unlike the design of permanent roads, for which a single speed parameter (i.e., design speed) is used for nearly all speed-dependent design decisions, an assortment of speed parameters is used in work zone design decisions. Numerous temporary traffic control decisions covered by MUTCD Part 6 (e.g., taper lengths, device spacing) are based on speed. In defining the “speed” term used in formulae, the MUTCD refers to “posted speed limit, or off-peak 85th percentile speed prior to work starting, or the anticipated operating speed.” This choice of speed values is applicable to the determination of sight distance. In the AASHTO design process, stopping sight distance and decision sight distance are computed using the design speed. Hence, the always complex topic of speed is further complicated in work zones. With this background, the survey sought to determine if the design speed approach was being applied to work zones and, if so, on what basis design speeds were selected. Establishing a design speed or another speed measure for construction work zones is a common but not universal practice among state DOTs. The survey indicated that 21 of the 32 DOTs responding to this question (66 percent) “often” establish a design speed or similar parameter for design of construction work zones. Another eight states (25 percent) “sometimes” establish a design speed or similar parameter for work zone design. Two responding states (6 percent) indicated they “never” establish a design speed for construction work zones. One state DOT did not respond to this question. A review of survey responses indicates that different states use a variety of speed parameters for construction work zone design. Various state respondents indicated that posted/regulatory speed, operating/prevailing/85th percentile speed, or the design speed of the highway being reconstructed was used as the starting point to set work zone design speeds. In some cases, reductions from this base value were determined appropriate. Hence there appears to be no single speed parameter that is consistently applied to the design of construction work zones. Given the variety of speed parameters that may be applied to a single MUTCD formula, it is not unexpected that states use a variety of speed measures in their guidance. Despite this, there does appear to be a widely shared goal with regard to speed accommodation in construction work zones. Nearly all responding states indicated a preference to provide work zone features that accommodate the same or similar speeds (i.e., the base value) as the affected road and to avoid design features necessitating speed reductions. Most states indicated that it is not always practical to accommodate the approach roadway or pre-project speed through work zones. In these cases, respondents indicated that reductions should be minimized. Ten state responses identified the goal of not reducing work zone speeds by more than 10 mph. Several of the same states indicated exceptions (i.e., larger reductions) to this criterion were sometimes needed. One state’s design manual indicates that work zone design speeds should not be less than 15 mph below the approaching road design speed. The MUTCD guidance on speed through work zones states “[a] Temporary Traffic Control (TTC) plan should be designed so that vehicles can reasonably safely travel through the TTC zone with a speed limit reduction of no more than 10 mph.” The state DOT survey responses are in close alignment with this guidance.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 33 The specific laws and procedures under which state DOTs establish (i.e., reduce) regulatory speed limits in work zones vary. The procedures used to determine if a reduction is appropriate vary as well. North Dakota DOT has developed a flow chart based on seven types of work activity and a series of factors (e.g., worker presence, lane width reduction) to determine if a speed reduction is appropriate. Indiana DOT has a complex set of guidelines. The guidance provides a table of suggested “Work Zone Special Limit (official action)” and “Work Site Speed Limit (Indiana statutes)” values for freeways based on facility type and pre-project speed limit. The work zone speed limit is determined based on the construction zone design speed, traffic volumes, construction work type, geometrics, project length, etc. The work zone speed limit should not exceed the construction zone design speed through the construction area. Indiana statutes permit the DOT to establish work site speed limits without an “official action.” The work site speed limit is the lesser of 45 mph or 10 mph below the original posted speed. North Carolina DOT did not respond to the survey. However, its Roadway Design Manual is available on the Web and indicates that the design speed of horizontal and vertical curves for crossovers and diversions on interstates and freeways should be equal or greater than the posted speed limit. Design speeds for median crossovers on expressways and major arterials with partial or no control of access may be lowered to 10 mph below the posted speed limit. Detour design speeds for facilities (arterials other than those indicated, collectors, local roads) should not be more than 10 mph below the posted speed of the existing roadway. Several states also commented that the work zone design speed was most pertinent to diversions and crossovers. South Dakota DOT has standard details for median crossovers that allow 45-mph, 55-mph, or 65-mph traffic to be maintained. The design manual indicates speed of traffic is usually reduced through and sometimes between the crossovers. Under the current Green Book design procedure, the selected design speed has a direct and indirect influence on numerous design features. (See the research at [37].) Criteria for sight distances, horizontal curvature, superelevation, vertical curves and clear zone width are directly related to the selected design speed. 3.2.2.2 Sight Distance The survey sought information on the stopping sight distance (SSD) criteria state DOTs apply to the design of construction work zones. States are divided on providing guidance for stopping sight distance in construction work zones. In response to the question, “Does your agency have stopping sight distance criteria for construction work zones?”, 14 states responded “no,” 16 states indicated “yes,” 1 indicated “yes/no,” and 1 did not respond. For those that do, there is substantial consistency in the approach, which is to select a speed parameter and use that as the basis for determining stopping sight distance in the same manner used for permanent roads. In most cases, this involves selecting the speed parameter (discussed previously) and applying Exhibit 3-1 from the

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 34 Green Book or MUTCD Table 6C-2, Stopping Sight Distance as a Function of Speed. Some state DOTs have not adopted the approach and values associated with the Green Book. This may reflect a deliberate decision not to change or the lag associated with revising guidance. For example, Virginia DOT uses the conventions (eye, driver height, range) and values associated with the pre-2001 AASHTO SSD policy, except that posted speed is used in lieu of design speed. Although, information specifically on SSD was solicited, several states provided additional information related to sight distance. Two states indicated the desirability of providing adequate visibility in advance of work zones, particularly tapers. One state commented, “The beginning of tapers should not be hidden behind curves.” New Jersey DOT traffic control details provide a table of Recommended Sight Distances to Beginning of Channeling Tapers for various regulatory speeds and settings (i.e., urban and rural). The values correspond to the decision sight distance values in the pre-2001 Green Book. The minimum and desirable Green Book values correspond to the New Jersey DOT urban and rural values. 3.2.2.3 Superelevation States were asked if they had guidance regarding superelevation of horizontal curves through construction work zones. Fifteen of the 32 states (47 percent) responded in the affirmative. Additionally, 4 of the 13 state DOTs that answered “no” provided insightful comments on their practice. Collectively, these responses indicate a variety of approaches to superelevation design and horizontal curve design for construction work zones on high-speed highways. These different techniques are grouped in the following summary. The most common reported practice is to use the same superelevation design practice for construction work zones as is used for permanent roads, based either on the Green Book or state DOT design manual. This requires further elaboration since the superelevation design practices for permanent roads vary among states. For high-speed facilities, the Green Book recommends that superelevation be distributed in accordance with Method 5. While this is the dominant practice among states for permanent roads, it is not universal. California DOT (Caltrans) uses a different superelevation design approach; the design values rely more heavily on friction than AASHTO Method 5. Responses such as “use AASHTO guidelines” and “follow AASHTO Green Book” were considered to mean the use of Method 5. In summary, the responses of seven states were interpreted to indicate that superelevation on horizontal curves for construction work zone roads is determined in the same way as it is for reconstruction and construction of permanent roads. Eight states were identified that use an approach different from the one they use to determine superelevation rates for new or reconstructed, permanent, high-speed roads. Three states explicitly indicated the use of AASHTO Method 2. Florida DOT has developed a table of minimum radii for a range of design speeds and normal crown. The radii values are based on limiting values of friction found in the Green Book. If a radius

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 35 less than the tabulated value is provided, the curve is superelevated. Montana DOT uses a similar method. The DOTs for Illinois and Indiana use Method 2 distribution for construction work zone roads. Colorado DOT also uses Method 2 distribution but with a different set of friction values. Two states were identified that use radii sufficiently large so as not to require superelevation. The minimum work zone road radius used by Mississippi DOT is one that can be provided without superelevation. Method 2 superelevation distribution is used to determine curvature-speed-superelevation relationships. Connecticut DOT uses the same approach. North Carolina DOT does not provide superelevation commensurate with the speed parameter and permanent road criteria. The North Carolina DOT Roadway Design Manual indicates that superelevation of interstate highway and freeway median crossovers cannot meet design speed standards due to existing restraints and it is more desirable to have lower superelevation rates that smoothly transition vehicles through the alignment than higher rates that have short lengths of change and that may create abrupt vehicle behavior. The South Dakota standard median crossover includes reverse curves with slope/superelevation of 2 percent (i.e., reverse crown). 3.2.3 Alignment Some work zone types rely exclusively on existing roads and do not involve the design of horizontal and vertical alignments. Other work zone types, such as diversions and median crossovers, involve temporary roadways that must be designed. The guidance obtained relates primarily to these work zone types. 3.2.3.1 Vertical Alignment Information from 17 state DOTs was obtained on some aspect of vertical alignment design for construction work zones. Five of the responses indicated that permanent road design criteria, using either AASHTO or their state design manual, were applied to work zones. Several state DOTs (e.g., Connecticut, Indiana) use 3R maximum grade criteria for work zones. North Carolina DOT has tabulated maximum grade value for detours based on speed. The two speed categories classified as high speed (46 to 55 mph and more than 55 mph) have maximums of 8 percent and 7 percent, respectively. Illinois and Indiana indicated that sag vertical curves are designed to meet the comfort criterion. One state indicated that vertical curves are designed to provide stopping sight distance based on the adopted design speed. The Vermont Agency of Transportation indicated that it attempts to provide vertical curves that correspond to the speed parameter’s criteria; but if this is not practical, it provides warning signs indicating the safe speed. Many state DOT work zone design publications do not address this topic directly. 3.2.3.2 Horizontal Alignment Horizontal alignment and, specifically, radius of curvature are closely associated with superelevation design. In several cases, the guidance and criteria for horizontal curvature are directly related to cross slope considerations (i.e., normal crown and

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 36 superelevation). Connecticut and Mississippi use the same general approach of limiting horizontal curvature to radii that may be normally crowned, including the provision of “negative” superelevation. Both states compute the minimum curvature that can be normally crowned using state-developed 3R criteria which, in both cases, involve Method 2 distribution. Florida and Montana DOTs use the same approach (but different from Connecticut and Mississippi). They tabulate values for the minimum radii for a specific design speed that may be normally crowned, based on Method 2 superelevation distribution. Radii may be less than those corresponding to normal crown, in which case superelevation is required. Three state DOTs have established maximum degrees of curvature for crossovers. Okalahoma and Oregon have established the maximum degree of curvature for median crossovers as 2 degrees, 30 minutes, and 2 degrees, respectively. Mississippi DOT uses a maximum of 1 degree, 30 minutes, for mainline crossovers on tangent sections. The South Dakota DOT standard median crossover uses 4-degree curves. 3.2.4 Roadway Cross Section Elements Construction work zones are often confined spaces. High speeds increase the potential for high-severity crashes as the separation between traffic and construction operations is compressed. Because of these conditions and the temporary nature of construction work zones, many states apply roadway cross section criteria to the design of construction work zone roadways that are different from what they apply to permanent roads. 3.2.4.1 Travel Lane Width The Green Book states, “Lane width of a roadway greatly influences the safety and comfort of driving.” Previous research conclusions (37,38) have established relationships between lane width and safety for two-lane rural roadways. Lane width determination is a decision that, implicitly or explicitly, must be made for virtually every construction work zone. Although lane width is often discussed as an isolated design feature, it should be considered in its complete context. The review found that state DOTs often consider a series of factors (e.g., number of lanes, single- or bi-directional travel, existence of a barrier) in determining appropriate width(s) for a particular application (e.g., crossover, detour, existing roadway). To form an accurate understanding of DOT practices, without posing excessively complex queries in the survey, two questions were prepared to garner information about travel lane and traveled way widths. In some cases, the responses to these two questions might appear incongruous. However, the context of the questionnaire was considered. One question invited numerical responses for a range of specific conditions. The other elicited narrative on how difficult and exceptional cases were addressed. The results reported below are an interpretation of the collective responses to the two questions. Guidance on numerical values for work zone travel lane width was obtained from 22 state DOTs, either from survey responses or guidance materials. As was stated in several responses and implied in nearly all others, DOTs prefer that construction work

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 37 zone travel lane widths meet the permanent road criteria for the affected facility. Several cases identified 12 feet as the desirable lane width. With varying degrees of stated reluctance, 14 states indicated using lanes as narrow as 10 feet under some circumstances. The following information elaborates on the responses from several of the 14 states that use 10-foot lanes under some conditions. Arizona DOT permits 10-foot lanes only “without lateral constraint”; the minimum with lateral constraint is 11 feet. Colorado DOT permits a 10-foot lane when the truck average daily traffic (ADT) is less than 50, the design speed is 45 mph or less, and there are no curves greater than 7 degrees (all criteria must be met). Colorado DOT also identifies specific criteria requiring a 12-foot lane. Florida DOT permits 10-foot lanes only on non-freeways; freeways require 11-foot lanes, and interstate highway lanes must be a minimum of 11 feet and at least one 12-foot lane per direction. Indiana DOT uses 10-foot lanes only on undivided highways; divided highways should be 11 feet; multi-way and multi-lane roadway widths should be 12 feet, and temporary crossovers should be 16.5 feet. Maryland State Highway Agency (SHA) generally uses an 11-foot minimum lane width for high-speed highways but may use as little as 10 feet. Nevada DOT has used 10-foot lanes for short distances and short durations without defining explicitly these distances and durations. Virginia has used 10-foot lane widths infrequently. Mississippi reported using lane widths as narrow as 10.5 feet. Alabama and Connecticut indicate 11 feet as their minimum lane width. Vermont uses 12-foot lanes for truck routes and narrower lanes on local roads, selectively. Most other states, in their responses or guidance, indicated hierarchies of preference (e.g., desirable, 12-foot; preferred minimum, 11-foot; absolute minimum, 10-foot); others make decisions based on specific project conditions. Some state DOTs have guidance that is dependent on the type of facility (e.g., existing road, temporary detour). The South Dakota standard median crossover provides for a 12-foot driving lane. 3.2.4.2 Traveled Way Surface Type The information indicated that travel lanes through construction work zones are nearly always paved. However, five state DOTs indicated using unpaved traveled ways to some extent. Connecticut DOT stated that unpaved travel surfaces are allowed only on non-limited-access facilities with ADT less than 15,000. Area type, truck traffic and operating speeds are also decision factors. These surfaces are used for a maximum of five days. Montana DOT has guidance on the type of surface to be provided on detour roads constructed specifically for the project. The guidance is reproduced here as Figure 5. Wisconsin DOT uses unpaved driving surfaces in construction work zones on low- volume roads when the duration of use is limited to several days. Texas DOT uses unpaved traveled way surfaces but did not elaborate on decision factors and limiting conditions. North Carolina DOT’s Web-accessible guidance indicated that temporary detours carrying an ADT of less than 750 should have unpaved surfaces and may be unpaved up to an ADT of 2,000.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 38 Missouri DOT uses structurally designed pavements for most work zone driving surfaces. However, for temporary bypasses that will be in place for only one season, a pavement consisting of a bituminous base mix material placed directly on the subgrade is used. Duration of Detour Operation Current ADT < 5 Days 5-30 Days 31 Days – 3 Months > 3 Months < 500 gravel gravel prime prime 500 – 1499 gravel prime prime PMS 1500 – 6000 prime prime PMS PMS > 6000 prime PMS PMS PMS GUIDELINES FOR SELECTION OF DETOUR SURFACING Figure 5. Montana guidance on surface type for detour roads constructed for project. 3.2.4.3 Shoulder Width Eleven state DOTs reported having guidance related to construction work zone shoulder width. Six respondents indicated that their agencies do not have guidance, and numerous others did not respond to this question, probably because no agency guidance on the subject exists. Additionally, guidance from two non-responding state DOTs (North Carolina, South Dakota) was found on the respective DOT Web sites. Shoulder width was highly dependent on the type of facility (e.g., existing roadway of divided highway; two-lane, two-way road; temporary road). The responses are summarized in Table 7. 3.2.4.4 Shoulder Surface Type Most state DOTs responding to the survey either indicated that their guidance did not address work zone shoulder type or did not respond to question. Mississippi DOT indicated construction work zone road shoulders are “usually gravel.” It is reasonable to conclude that when non-paved driving surfaces are provided (as indicated by five responding DOTs), shoulders are constructed of the same material. North Carolina provides minimum shoulder widths of 4 feet, 2 feet of which are paved. 3.2.4.5 Barrier Offset It is not uncommon for a barrier system to be placed adjacent to construction work zone roadways. The “shy distance” is the limit of where a roadside object will be perceived as an obstacle by the typical driver to the extent the driver will change the vehicle’s placement or speed. It is measured from the edge of the traveled way. The Green Book recommends that a 2-foot offset be provided where a roadside barrier, wall or other vertical element adjoins shoulders. As reported in section 3.1.3, the Roadside Design Guide Chapter 9 also recommends a 2-foot offset to portable concrete barrier. In

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 39 construction work zones, shoulders may be narrow or non-existent. Some state DOTs address barrier offsets in their construction work zone design practices. For certain types of lane closures on divided multi-lane highways, Arizona DOT’s minimum travel lane width is 10 feet if unconstrained and 11 feet if constrained. The DOTs of Alabama, Missouri and Nevada strive to offset barriers 2 feet from the traveled way. Virginia DOT reported that barriers are normally placed from 0.5 to 1 foot from the traveled way edgelines. Table 7 Summary of construction work zone shoulder width guidance Shoulder Width (ft) Divided Highway State DOT Right Left Undivided Highway Unspecified Alabama 4 Arkansas 2 California 10 5 Connecticut 2 2 1 Illinois 2 2 1 Indiana 2 2 1 a Iowa 3 b DHV Minimum Mississippi < 200 > 200 3 c 5 c DHV Desired North Carolina 4 d 4 d 4 d < 100 100-400 > 400 4 e 6 e 8 e Oregon 2 Virginia 10 <10 South Dakota 4 f Wisconsin 2 – 3 2 - 3 5 g West Virginia 10 DHV = design hour volume. a runarounds: 6 feet, left and right; one-lane temporary crossovers: 5 feet, left and right; multi-way and multi-way operations: 5 feet, left and right. b information in table is for detours and based on review of Web-accessible design manual; survey response indicated no guidance on subject. c applies to two-lane, two-way diversions and detours. d minimum for crossover and detours associated with all functional classes. e graded width for detours carrying local roads, collectors and minor arterials. f applies to median crossovers. g applies to left and right shoulders of single-lane crossovers.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 40 3.2.4.6 Shoulder Rollover The algebraic difference between the slopes of a traveled way and adjoining shoulder can affect vehicle operations. For permanent roads, the Green Book recommends that this “rollover” (also know as “breakover”) be limited to 8 percent. The crown between adjoining cross slopes can be limited by rounding between the opposing- direction slopes. The survey sought information on state DOT practices regarding maximum rollover values in construction work zones. The majority of survey respondents either did not respond or stated they have no guidance on the subject; 13 states did provide a response. Colorado DOT indicated it was practice to extend the superelevation across shoulders, thereby eliminating the rollover. West Virginia DOT uses its “standard” rollover. Vermont stated that construction shoulders are too narrow to be a concern. Five state DOTs reported using AASHTO guidelines, presumably an 8 percent maximum. Oregon DOT uses a 4 percent maximum rollover. Two states reported using a 5 percent maximum. New Hampshire DOT uses a maximum of 6 percent, while Alabama and Mississippi indicated a 7 percent maximum. Arkansas was the only respondent specifically citing a maximum value of 8 percent. 3.2.5 Roadside and Barrier Placement Adoption of the roadside safety principles and the implementing procedures outlined in the Roadside Design Guide has significantly enhanced highway safety. The concepts of forgiving roadside, clear zone, prioritized treatment of hazards, and crashworthiness are applicable to work zones as well as permanent roads. There are also very significant differences between permanent roads and construction work zones. First, more people (i.e., workers) are proximate to high-speed facilities while the facilities are under construction/reconstruction. Roadside design of permanent roads does not address protection of people from vehicular traffic. Additionally, roadside hazards in the form of construction equipment and work site features (e.g., slopes, drop-offs, unshielded structures) are subject to frequent change. Consequently, construction work zones involve some unique roadside design considerations, which are recognized in a chapter of the Roadside Design Guide devoted to work zones. State DOT policy and guidance documents and survey responses generally reflect this expanded range of factors. The order of preference in the Roadside Design Guide for addressing roadside obstacles (i.e., removal, redesign) is based on safety efficacy and does not address practicality or cost-effectiveness, both of which must be considered. Hence, several conventions and terms that are applied to roadside design for permanent roads, such as clear zone distances and barrier warrants, may be interpreted differently for permanent roads and work zones. The unique context of construction work zones and its influence on design decisions is generally recognized by state DOTs. Several states have established very specific guidance, and others rely on more general advice and principles. The review of state DOT documents on this subject produced conclusions that are consistent with those reported in the Roadside Design Guide and summarized in section 3.1 of this chapter. The summary of state DOT practice is outlined in three categories.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 41 3.2.5.1 Clear Zone Caltrans uses the same roadside guidance for work zones and permanent roads. This guidance addresses, but does not explicitly define clear zone distances. A clear recovery area 20 feet wide “on conventional highways is advised.” Designers are further advised to consider a variety of site-specific factors in determining the clear zone distance. Work zones are not specifically mentioned. Colorado DOT establishes detour clear zone distance on the basis of speed, geometry and traffic. Connecticut DOT determines clear zone width by applying the design speed adopted for the work zone to its clear zone guidance for permanent roads. The guidance relies on the set of variables presented in the Roadside Design Guide Table 3-1. Virginia DOT determines work zone clear zone distance on the basis of speed. Illinois DOT identifies specific features (e.g., drop-offs) that require consideration of positive protection; its guide to determine clear zone distance is included as Figure 6. The processes for determining clear zone distance of the state DOT of Illinois is based on speed, traffic, and slope. 3.2.5.2 Barrier Placement Guidance Two general conditions were identified for which barriers are routinely placed. One is part of the roadside design strategy to shield errant vehicles from roadside hazards (i.e., fixed objects, critical slopes and drop-offs) and people, particularly construction workers. The other general category of barrier use is to separate vehicle paths. The Roadside Design Guide defines “warrants” as “the criteria by which the need for a safety treatment or improvement can be determined.” This term will be avoided here only because some people may infer a rigid relationship between a condition and barrier placement. Instead a summary will be presented of guidance used by state DOTs as to where longitudinal barriers or other shielding devices should be provided. Some DOTs have guidance that is very specific, but most have more general information. No state DOT has guidance that addresses every situation; varying degrees of judgment are necessary to implement all the guidance documents reviewed. The most deterministic policies are those based on definitive clear zone distances, identification of hazards, and declarative guidance for treatment of hazards within the clear zones. For example, the section of the North Carolina DOT Design Manual addressing the use of detours and crossovers for maintenance and protection of traffic states, “The clear zone and recovery area should be maintained in accordance with the Roadside Design Guide or protected by guardrail or concrete median barrier.” This is the most deterministic guidance found.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 42 CLEAR ZONE DISTANCES (ft) (Construction Projects) Figure 6. Excerpt from Illinois DOT design guidance. Front slopes Back slopes 1:6 or flatter 1:5 to 1:4 1:3 1:3 1:5 to 1:4 1:6 or flatter Approach posted speed limit ADT Work zone clear zone distances (ft) Under 750 4-6 4-6 4-6 4-6 4-6 750-1500 6-8 8-10 6-8 6-8 6-8 1500-6000 6-8 10 8-10 8-10 8-10 35 mph or less Over 6000 10 10-12 10 10 10 Under 750 6-8 6-10 4-6 4-6 6-8 750-1500 10 10-14 6-8 8-10 10 1500-6000 10-12 12-16 8-10 10 10-12 35-50 mph Over 6000 12-14 16-18 10 12 12-14 Under 750 6-8 10-12 6 6-8 6-8 750-1500 10-12 12-16 6-8 10 10-12 1500-6000 12-14 16-18 10 10-12 12-14 55 mph Over 6000 14-16 16-20* 10-12 12-14 14-16 Under 750 10-12 12-16 6-8 8-10 10 750-1500 12-16 16-20* 8-10 10-12 12-14 1500-6000 16-18 20-24* 10-12 12-14 16 60 mph Over 6000 18-20* 22-28* 12-14 16 16-18 Under 750 12 12-16 6-8 10 10 750-1500 16 18-22* 8-10 12 12-14 1500-6000 18-20* 22-26* 10-12 14-16 16-18 65 mph Over 6000 18-22* 24-28* ** 14-16 16-18 18 * Clear zones may be limited to 18 feet for practicality. ** Use guidance for permanent roadways. Notes: • All distances measured from edge of traveled way. • For clear zones, the ADT will be the total ADT on two-way roadways and the directional ADT on one-way roadways. Traffic volumes will be expected traffic volumes through the work zone. • The values for back slopes apply only to a section where the toe of the back slope is adjacent to the shoulder. For roadside ditches, use permanent roadway guidance. • Approach posted speed is approach posted speed prior to the work zone.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 43 Colorado DOT provides barriers when any hazards exist within the clear zone of a detour. Under Connecticut DOT design guidance, if the recommended clear zone cannot be achieved, the safest treatment should be provided consistent with cost-effectiveness and geometric considerations. The traffic barrier placement guidance of Indiana and Montana DOTs are similar. Both DOTs have a procedure for establishing clear zones. They also indicate that due to the limited time exposure, it may not always be cost effective to meet the permanent installation criteria. Both DOTs also indicate that the designer must use considerable judgment when applying the clear zone distances, due to the hazardous conditions that typically exist in construction zones. Indiana DOT identifies 9 location types where the provision of positive protection should be considered and 13 factors that should be considered in the placement decision. Virginia DOT uses a process to address hazards within the clear zone that considers the hazard type (i.e., fixed object, slope), speed and exposure (length and duration). Florida DOT guidance indicates that barriers serve four specific functions: 1) protect traffic from entering work areas, such as excavations or material storage sites; 2) provide positive protection for workers; 3) separate two-way traffic; and 4) protect construction such as falsework for bridges and other exposed objects. However, specific placement guidance is not provided. Designers are charged with anticipating “when and where barriers will be needed.” The Missouri DOT’s draft guidance calls for barrier placement in conjunction with bridge rail replacement and full-depth deck repair activities. Oregon DOT identifies other specific conditions for which barrier placement should be considered if the conditions will be exposed to traffic for more than five days. A number of state DOTs have general guidance that either augments more specific guidance or stands alone. Some DOTs indicated, without further elaboration, that barrier placement decisions are determined on a case-by-case basis. Other DOTs identified factors (e.g., speed, volumes, duration of exposure, distance from traveled way) that should be considered in decisions. Although several state DOTs, such as Florida DOT, identified worker safety as a consideration in barrier placement decisions, no specific guidance on this subject was found. The practice of installing barriers to separate two-way traffic on a single roadway of a normally divided highway was found to be widespread. For some responding state DOTs (e.g., Michigan, New York), this was the only reported situation for which barrier placement was routinely provided. 3.2.5.3 Traffic Barriers Information on traffic barrier types and installation details is available in the design guidance, construction details, and standard drawings of many states. Temporary (portable) concrete barrier is the dominant type, for which there are many dimensional and structural variations. When DOT publications referred to “positive” separation, it was interpreted to mean rigid concrete barrier. Other longitudinal roadside systems, such as the semi-rigid W-beam, are also used but far less frequently. Many details of taper ratios,

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 44 anchorage systems, and end treatments are available and were reviewed. The Roadside Design Guide Chapter 9 and other resources provide detailed information on crashworthiness requirements and the performance of individual systems. Therefore, these details are not considered appropriate for this report, and a summary is omitted here. A number of state DOTs are actively developing or revising their roadside design policies and guidance. Illinois DOT indicated that it is developing a policy to determine where temporary concrete barriers should be placed. As described earlier, Missouri DOT has developed draft guidance that identifies recurring conditions for which barriers should be provided. Virginia DOT has a roadside design policy specifically for work zones. The policy is being revisited. Wisconsin DOT is presently using interim guidance and information from research reports for roadside design and traffic barrier placement decisions. 3.2.6 Ancillary Design Information 3.2.6.1 Drainage There are several basic purposes of highway drainage, including the rapid evacuation of moisture from the driving surface, prevention of pavement structure saturation and maintenance of the hydrologic systems traversed by the roadway. Drainage design for construction work zones has similar purposes, although draining the subsurface of temporary pavements is not emphasized. Erosion and sediment control, bank protection, and storm water management are important design considerations for construction work zones. However, these issues are generally regarded as part of project permitting and environmental management. The requirements and guidance vary substantially by jurisdiction. As such, no information was sought on these subjects. Less information on drainage practices was elicited through the survey than other topics; 9 of the 32 responding DOTs (28 percent) indicated having guidance on design practice for construction work zone drainage. However, the responses and guidance publications provide information on significant points associated with this topic. Maintaining a well-drained driving surface during and after construction is an important consideration for any project. Many of the same factors associated with designing a drainage system for a permanent road are considered. However, the abbreviated service life of the roadway has direct implications for the specific criteria applied to drainage structures. State DOT guidance was found on the following topics: Drainage of temporary roads. For projects that include detours, crossovers and other supplemental driving surface, drainage schemes and structures are usually required. The preponderance of survey responses provided information on the design criteria for temporary roads and attendant drainage works. A basic decision in designing a hydraulic structure is the selection of a design frequency or recurrence interval. This selection is based on cost and risk considerations, and design frequencies for various types of

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 45 structures are generally included in state DOT drainage manuals. Major structures (e.g., bridges and culverts associated with arterial highways) are designed for infrequent events (i.e., 25 to 100 years). When the capacity of these structures is exceeded, significant disruption and losses result. Therefore, it is cost-effective to design these structures for events that are exceeded very rarely. On the other hand, less important crossings and roads (e.g., median drain of a collector) are designed with the recognition that the hydraulic capacity will be exceeded with greater frequency but less dire consequences. The results of the survey indicate a mix of practices regarding the selection of design frequencies for temporary drainage structures. Several states indicated using the same criteria as permanent facilities; several others indicated using two-year frequencies. The AASHTO Model Drainage Manual (39) suggests that drainage systems for detours and temporary roads be designed for a two-year frequency, if the roadway is required for a year or less, and a five-year frequency, if it is required for more than a year. The differing practices of state DOTs may not be a matter of great practical significance. Often, DOTs establish minimum diameter pipes and culverts based on other-than-hydraulic considerations (e.g., debris, maintenance). The design of many structures is controlled by minimum size rather than hydraulic capacity. Extension and continuation of existing drainage systems. The Florida DOT publication, Temporary Drainage Design Handbook, was the only state DOT guidance found that addresses temporary base drains, extending culverts, and exercising care to avoid drainage diversions. Construction staging considerations. When maintaining traffic on existing driving surfaces and reconstructing facilities in place, the goals of drainage design may be achieved through thoughtful sequencing and near replication of the existing drainage structures. While no unique hydrologic or fluid mechanics techniques are needed, careful review and application of drainage principles can avoid the accumulation of water on a driving surface. Florida DOT has published guidance to address several potentially problematic situations. Guidance is provided on milling pavements to prevent runoff from the closed/milled lane onto the traffic lane. If not properly sloped, turnouts can result in ponding adjacent to the travel lane. Sandbags used as temporary curbing and temporary inlets for positive drainage are suggested remedies. An equation and implementing guidance are also provided for computing spread (the lateral limit of flowing water) adjacent to temporary concrete barriers. These can be used to assess travel lane encroachment, and, if excessive, provide additional relief. 3.2.6.2 Turnouts Turnouts or pull-offs are refuge areas within construction work zones that have narrow or non-existent shoulders. Information on agency practices regarding provision, spacing and configuration of these refuge areas was solicited through a survey question. Eleven of the 32 responding DOTs (34 percent) indicated their agencies “never” provide turnouts in construction work zones. Thirteen state DOTs (41 percent) “sometimes” use turnouts, and six others (19 percent) do so “often.” One state DOT reported

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 46 “often/sometimes” use. One state did not answer this question. In terms of design guidance, most of the 20 DOTs that provide turnouts with some frequency (often or sometimes) did not indicate specific criteria (e.g., traffic volumes, facility types) where turnouts are provided. There were numerous references to case-by-case determinations. Maryland generally provides turnouts when a shoulder is closed for a half mile or longer. Oregon DOT uses the passing and climbing lanes that are part of their sometimes long and winding permanent roads to provide turnouts. Pennsylvania and Vermont space pull- offs at approximately half-mile intervals. Wisconsin DOT uses a spacing of half to three quarters of a mile. The length of Wisconsin DOT pull-offs is approximately 150 feet plus tapers. Virginia DOT provides turnouts infrequently and primarily on high-trafficked interstate projects. It is investigating expanded use of these features and development of a policy. New York DOT provides pull-offs on the median side of facilities carrying two- lane, two-way traffic on a single roadway of a normally divided highway; typical spacing is 1 mile. 3.2.6.3 Visual Barriers The use of devices to improve visibility and focus within construction work zones is common. Glare screens are longitudinal systems intended to prevent or reduce the adverse effect of headlights on opposite-direction-driver vision. There are several types of designs, including vertically extended concrete traffic barriers and manufactured products that are installed on top of temporary precast concrete barriers. A separate type of visual screen is sometimes used to inhibit driver visibility of work zones, and thereby reduce potentially detrimental distraction from the driving task. These installations are sometimes referred to as “gawk screens.” Responses to the survey indicate that 5 of 31 states responding to this question (17 percent) use visual barriers “often”; 20 states (60 percent) reported using them “sometimes,” and six responding DOTs (23 percent) indicated “never” using visual barriers. Most of the narrative comments referred to considerations associated with glare screens. Several states indicated that glare screens are used most frequently at locations susceptible to unusual headlight glare (e.g., horizontal and vertical curves, crossovers). Another common application is between opposing-direction traffic lanes, often when two-way traffic is on a single roadway of a normally divided highway. Pennsylvania DOT uses temporary concrete barrier with a height of 52 inches, except at locations where a barrier of less height is used to improve stopping sight distance. Nevada DOT decides on use/non-use based on location, traffic volumes, etc. It has found that temporary screens are effective in some cases and a problem in others. Two responding DOTs addressed the use of barriers that inhibit driver visibility of the construction area. Maryland installs these systems if construction activity is expected to result in significant distraction of road users, especially on high-speed roadways. Oregon attaches plywood atop temporary concrete barriers “to keep drivers focused on the road ahead and not on the roadside construction.” Guidance on when this system is installed was not provided.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 47 3.2.6.4 Interchange Speed Change Lanes Construction work zones that encompass interchanges involve considerations and decisions beyond those associated only with segments. Interchanges are locations of potential conflicting movement and place high demands on driver performance. In addition to directional and/or lane changes, significant speed changes and speed variance occur within interchange areas. Acceleration and deceleration lanes facilitate the transition from crossroads to the mainline and vice versa. A design objective is to minimize the speed disparity between mainline and entering/exiting traffic streams. However, providing speed change lanes in work zones is often difficult. The survey sought information on state DOT practices regarding the design of temporary interchange arrangements on three specific features: acceleration lane length, deceleration lane length, and yield verses stop control, including signing practices. The responses required some interpretation, since several made general references to use of the Green Book, MUTCD and standard drawings. A reference to the Green Book was considered to mean that the respondent applied the acceleration and deceleration lane length criteria found in Chapter 10 (i.e., Exhibits 10-70 and 10-73). The MUTCD Part 6 provides typical applications that illustrate general configurations and traffic control devices. Some of these address work zones that include and involve ramps and speed change lanes and associated signing. The MUTCD illustrates entrance and exit configurations but does not provide acceleration and deceleration lane lengths. With this background, four state DOTs indicated using the Green Book and/or MUTCD to determine speed change lane length and signing. In general, only a few state DOT publications (e.g., policy, drawings, written guidance) were identified that address speed change lane geometry within construction work zones. The MUTCD and several state DOT manuals provide information on traffic control policy and practice. Arkansas DOT reported that it does not provide acceleration lanes to maintain traffic. Caltrans referred to its standard drawings, which illustrate options for closing exit and entrance ramps and temporary provision. Figure 7 illustrates two examples; the lengths of acceleration and deceleration lanes are not provided. Connecticut DOT attempts to provide acceleration lane lengths that meet the permanent highway criteria for the work zone design speed. Maryland traffic control details include a figure to determine acceleration lane length on the basis on mainline design speed and ramp speed, with adjustments for ramp grades over 2 percent. Michigan DOT’s informal guidance is to provide a minimum length of 300 feet. New Jersey DOT’s guidance is to provide the same length acceleration lane as existed without the work zone. Oregon DOT strives to provide 70 percent of the length that would apply to a permanent facility/condition. Virginia DOT attempts to provide the pre-project acceleration lane length.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 48 Figure 7. Examples of temporary interchange access points (Caltrans). Some DOTs relate the use of YIELD and STOP signs at interchange entrance ramps to acceleration lane length. Alabama DOT installs YIELD signs on acceleration lanes that do not meet the minimum criteria; STOP signs are provided when there is no acceleration lane. Arkansas provides a YIELD or STOP sign when the acceleration lane length is less than the Green Book value. Indiana DOT employs additional traffic control devices on acceleration lanes if the length is less than indicated by its guidance. Maryland SHA uses a Yield Sign Warrant Checklist. If the acceleration lane length is less than the value criteria (described in previous paragraph), a YIELD sign is provided. New Jersey DOT installs YIELD signs in conjunction with acceleration lanes. If no acceleration lane is provided, the decision to place either a YIELD or STOP sign is made on a case-by-case basis. Wisconsin DOT does not install YIELD signs at locations where the mainline has more than one lane open to traffic and the taper is as long as that of the pre-project condition. West Virginia DOT’s Traffic Control Manual provides conditions for the use of YIELD and STOP signs for entering normally divided highways under different work zone conditions. Examples of both entry and signing conditions associated with yield and stop control are included as Figures 8 and 9. The MUTCD Part 6 includes a set of typical applications (TA-40 to TA-44) illustrating signing and other traffic control associated with temporary interchange ramp connection arrangements.

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 49 Figure 8. Example of entrance ramp with YIELD sign (West Virginia DOT). Figure 9. Example of entrance ramp with STOP sign (West Virginia DOT). The New Jersey DOT traffic control details indicate a combined length of 500 feet for the taper and deceleration lane on divided highway interchanges. Wisconsin DOT

Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved. 50 uses 200-foot exit tapers and 200-foot deceleration lane lengths when necessary within construction work zones. 3.2.6.5 Large Vehicle Accommodation Most state DOTs responding to the survey consider oversize vehicles in designing construction work zones on high-speed highways, with 23 (72 percent) responding “yes” to this question and 9 (28 percent) indicating “no.” Most of the efforts associated with oversize vehicle accommodation are related to intra-agency coordination. Numerous DOTs reported having procedures in place to coordinate between affected organizational units (e.g., construction, design and permits). In some cases, DOTs will refrain from issuing permits for oversize vehicles to traverse a particular route segment if the available clear width is at or below some value. States have different threshold width values (e.g., 14.5, 15, 16 feet) for permit issuance restrictions. The Wisconsin DOT procedure is unique and summarized here. Permits for oversize vehicles are not route specific. Vehicles wider than 8.5 feet require permits; the maximum vehicle width permitted is 14 feet. The design function of the DOT attempts to provide a minimum travel width of 15 feet to accommodate all vehicles. If the 15-foot width is not provided, advance warning signs are posted prior to the last interchange exit before the start of the width restriction, and they direct vehicles to exit. Six respondents indicated that signs were placed to indicate restricted road conditions and alternate routing. One respondent (Alabama DOT) provides wider pavements for abnormal volumes of oversize vehicles. 3.2.6.6 Review of Contractor Traffic Control Plans There is a very high degree of consistency in the general approach of state DOTs to consideration of contractor-developed traffic control plans. The DOTs of Illinois and Iowa are exceptions to the general pattern; they do not permit contractors to submit alternative traffic control plans. All other responding states do. The dominant model is that a DOT-developed traffic control plan is included in the contract drawings. The contractor may submit an alternative plan, which may only be implemented following its approval by the DOT. Oregon DOT has a unique contracting requirement. The contractor for every project must submit a traffic control plan, even if it is a letter indicating the intention to implement the DOT plan. The procedures for reviewing alternative, contractor-developed traffic control plans vary among states in terms of submission time frame and internal DOT review/approval roles. Two states (Alabama and Indiana) indicated that the cost of the contractor’s alternative plan is limited to that of the original plan. The Michigan and New York State DOTs review contractor traffic control plans as value engineering proposals.

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 581: Design of Construction Work Zones on High-Speed Highways explores an approach for the selection of an appropriate construction work zone type; offers suggested guidance for the design of geometric features, including horizontal and vertical alignment, cross-sectional features, and barrier placement; and examines a variety of ancillary features such as drainage systems, lighting, and surface type. The contractor’s final report on the research activities used to develop NCHRP Report 581 has been published as NCHRP Web-Only Document 105. As part of the research associated with this activity, a work zone prediction model and user's guide was created to help estimate free-flow vehicle speeds through two types of construction work zones on four lane freeways--single lane closures and median crossovers.

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