Design of Construction Work Zones on High-Speed Highways (2007) / Chapter Skim
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From page 18... ...
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.
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From page 19... ...
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.
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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.
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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.
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. The guidance also imparts flexibility and discretion in dealing with construction work zones ("to the extent that existing roadside conditions allow")
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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)
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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.
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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.
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For long-term construction work zones, the capacity values are based on research in (31) and shown in table 6.
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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)
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, 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.
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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.
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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.
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Figure 4. Sample work zone type feasibility chart (Connecticut DOT)
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From page 32... ...
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.
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33 The specific laws and procedures under which state DOTs establish (i.e., reduce) regulatory speed limits in work zones vary.
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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.
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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.
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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.
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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.
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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)
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From page 39... ...
39 construction work zones, shoulders may be narrow or non-existent. Some state DOTs address barrier offsets in their construction work zone design practices.
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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.
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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.
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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.
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From page 43... ...
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.
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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.
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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.
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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.
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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.
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From page 48... ...
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.
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From page 49... ...
Final Report for NCHRP Report 581: Design of Construction Work Zones on High-Speed Highways Copyright National Academy of Sciences. All rights reserved.
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From page 50... ...
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)
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