Guidelines for Implementing Managed Lanes (2016) / Chapter Skim
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Pages 36-74
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From page 36... ...
36 Design Elements Overview This chapter provides guidance and relevant discussion of a variety of elements that need to be considered in the development and design of a managed lane facility. While aspects of some of the topics in this chapter are also covered in other chapters (e.g., planning and policy decisions, appropriate traffic control devices)
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From page 37... ...
37 and limited sight distance, then large commercial trucks will likely be excluded as a design vehicle. A private developer or a public–private partnership should carefully identify the likely users of the managed lanes, as well as their likely effects on revenue.
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38 completed. When bus volumes are high, a bus-only lane might be desirable.
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39 (necessitating walls or screens) , and they require more width.
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40 • Single-unit truck -- SU. • Intermediate semitrailer -- WB-40 (40-ft wheelbase)
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41 manner. Motorists benefit not only from having consistency between a managed lane and the adjacent infrastructure but also from having design consistency across all facilities within the region or area.
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42 applicable PBPD-related policies and programs that are in place within the jurisdiction of the project. More information on PBPD principles and related resources can be found through FHWA (66)
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43 information is provided for general reference only. The practitioner should determine what national, state, or local standard applies to a particular facility.
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From page 44... ...
44 In addition to the cross-section elements described in the previous list, there are additional design elements that are also considered in context as the design of the managed lane facility is developed. A selection of those elements and their effects on managed lane operations are listed below: • Horizontal alignment -- The radius of horizontal curvature used in a particular roadway design is a function of design speed, rate of superelevation, and side friction with practical limits due to right-of-way constraints (6)
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From page 45... ...
45 stopping sight distance criteria is usually sufficient from the viewpoint of comfort and appearance. For sag curves, the use of the stopping sight distance criteria for establishing minimum rates of vertical curvature is recommended.
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From page 46... ...
46 in their own respective sections of this and other chapters, but a selection of items are compiled here to provide examples of operations that can be affected by reduced lane or shoulder widths: • Any hardware or equipment placed in the median (where there is no full-width shoulder or built-in maintenance access) or overhead will require lane closures for access to complete maintenance, which equates to a loss of operational time, particularly as the equipment ages (for more information, see the section later in this chapter on providing for associated equipment and devices)
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From page 47... ...
47 operating conditions on the facility (see sections on buffer separation, pylon separation, and emergency refuge areas, as well as Table 5)
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From page 48... ...
48 it is important to consider the peak-hour directional split to ensure that sufficient capacity is available in the off-peak direction to allow one lane from the off-peak direction to be shifted to the peak direction without creating congestion in the off-peak direction. Separation Between Managed Lane and General-Purpose Lanes There are multiple ways to provide separation between managed lanes and the general-purpose lanes of a freeway.
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From page 49... ...
49 least 20 ft (71) so that the design can accommodate two sideby-side vehicles in case of crashes or other incidents.
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50 – Sight distance improvement -- no wall obstruction is present. • Pylon disadvantages: – Ability of motorists to travel from general-purpose to managed lanes (or vice versa)
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51 where significant peak-direction volumes can be collected and distributed to other roadways. With this treatment, barrier-separated travel lanes are assigned to one direction of travel during a peak period (e.g., inbound traffic during the morning peak)
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52 flexibility to provide capacity in the direction of travel that needs it most. An example of such a facility is the I-30 corridor east of downtown Dallas, Texas (see Figure 35)
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53 Source: Caltrans (53)
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54 than 23 ft)
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55 Source: Google EarthTM. Figure 39.
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56 assembly. The horizontal clearance, especially in the median for median-located facilities, should be such that anticipated users can drive past gantries without deviating from the travel way; similarly, the vertical clearance must be generous enough that the truck or bus traffic will be able to safely pass underneath gantries or other toll collection hardware.
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57 Source: Adapted from Perez and Sciara (78) , Figure 10.
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58 the HOV lanes, the design will have to accommodate both the new ramps and the connections to them. In particular, if a facility changes from at-grade access to grade-separated access, the design must have sufficient cross section to include the transitions and speed-change lanes associated with the new grade-separated ramps.
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From page 59... ...
59 est priority (67) , and such effects should be identified through a formal operational analysis (35)
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60 some operators of managed lane facilities may have policy directives that specify analysis tools to be used, and those applicable policies should be considered in the planning process as well. A Minnesota study (81)
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61 chosen varied from one facility to another. Similar considerations of applicable policies and safety or performance goals must be made when planning for new or revised access points.
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62 California guidance (35) mandates that the type and location of proposed access openings shall be determined by an operational analysis.
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63 distance equivalent to 1000 ft per lane change required to enter the managed lane from the nearest entrance ramp. The design should also include accommodation for structures for advance signing upstream of the managed lane(s)
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From page 64... ...
64 The weave zone should be longer than the minimum shown in Figures 48 and 49 if the design vehicle is a bus or if a high volume of such vehicles is anticipated. If a merge area is sufficiently long, it may be used as a passing zone for managed lane facilities with just one lane (83)
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From page 65... ...
65 A shortcoming noted on some projects is drivers attempting to use such ramps to both enter and exit; pavement markings should clearly define whether the ramp is intended for entrance or exit, and application of pylons or concrete barriers may be necessary to prevent unintended movements. Intermediate-Access Treatments -- Direct Access Similar to traditional freeway entrance/exit ramps, direct (grade-separated)
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From page 66... ...
66 facilitate access, the design of the roadway must provide sufficient cross section for the lanes needed to accommodate the anticipated volumes for each movement. The ramp must be long enough to minimize the potential for queue spillback from the ramp into the managed lane, and sufficient signing must be provided in advance of and at the access point to inform drivers which direction is the mainline since the ramp is located on the left instead of the right.
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From page 67... ...
67 Source: Nevada DOT, Planning Division, Safety Engineering Section (54)
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From page 68... ...
68 treatments, and the cross section of the facility must provide sufficient width to accommodate the selected treatment. The design should also include accommodation for structures for advance signing upstream of the terminus of the facility and needed signing at or downstream of the end of the facility (see the following section on operational impacts on design for more information)
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From page 69... ...
69 In the draft chapter (87) , speed-flow diagrams were calculated and provided for each facility type.
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From page 70... ...
70 infrastructure and communications abilities to communicate the current toll to drivers. Additional discussion of appropriate infrastructure can be found in Chapter 6 in the section on toll collection system operations.
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71 All of the priced managed lane toll zone components need appropriate access for preventive maintenance and other infield needs. To provide this access, all components should be housed collectively in hardened and protected utility cabinets with sufficient controls to prevent tampering, promote safety for maintenance personnel, and provide easy access.
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From page 72... ...
Source: Colorado DOT (88)
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From page 73... ...
73 the specific needs of a particular facility when determining what elements to include in an enforcement design. Literature on this topic, as it pertains to the design implications for implementing managed lanes, can be found in the tables in the eligibility validation and enforcement sections within the operations and maintenance chapter (Chapter 6)
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From page 74... ...
74 operate in the opposite direction of evacuation flow to allow responders to enter the evacuation area. Incident strategies will be based on the needs of the facility and the community the facility serves.
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