A Guidebook on Transit-Supportive Roadway Strategies (2016) / Chapter Skim
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Pages 66-110
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From page 66... ...
66 This chapter is the second of four toolbox chapters presenting potential strategies for improving bus speeds and reliability. The strategies presented in this chapter require the participation of the roadway agencies responsible for traffic control devices, and sometimes other agencies, but are generally less infrastructure-intensive than the strategies presented in the following two chapters.
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From page 67... ...
Traffic Control Strategy Toolbox 67 • Roadway agency access management policies exist that divert left-turn movements to signalized intersections; • Boulevard-type street treatments with raised landscaped medians exist that prevent left turns; and • Allowing vehicles to make the turn could generate undesired through traffic within a neighborhood or district. At the same time, allowing buses to make these movements may allow a more direct routing that would save travel time or provide bus service closer to passengers' origins and destinations.
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68 A Guidebook on Transit-Supportive Roadway Strategies policy may be required. If infrastructure is being modified (e.g., creating a median opening for a bus-only turn lane)
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Traffic Control Strategy Toolbox 69 6.2 Turn Restrictions Description One or more existing general traffic turning movements at an intersection are prohibited. Purpose Turning movements at intersections can cause delay for buses and other intersection users when: • No turn lane is available, and vehicles wishing to continue straight must wait for a vehicle to make its turn before they can proceed; • Protected left-turn phases (i.e., left-turn arrows)
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70 A Guidebook on Transit-Supportive Roadway Strategies Constraints A key consideration is the availability of a suitable alternate route for the diverted traffic. Suitability criteria can include traffic operations, safety, compatibility with adjacent land uses, and diversion distance.
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Traffic Control Strategy Toolbox 71 Implementation Guidance A traffic engineering study will be necessary to quantify the impact of the proposed change on bus and general traffic operations and on safety. Delay impacts are suggested to be quantified on both a vehicle-delay and person-delay basis.
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72 A Guidebook on Transit-Supportive Roadway Strategies enforced. Whether a suggestion or a legal requirement, an outreach campaign may be necessary to raise public awareness of the issue.
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Traffic Control Strategy Toolbox 73 nurturing a more friendly and courteous environment between bus operators and motorists" (King 2003)
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74 A Guidebook on Transit-Supportive Roadway Strategies • Allocating more green time to approaches used by buses (which can potentially include minor-street approaches and left-turn lanes)
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Traffic Control Strategy Toolbox 75 Cost Considerations • Planning and coordination costs. Moderate for a corridor, requiring collecting traffic demand data at each intersection (including for buses, bicyclists, and pedestrians)
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76 A Guidebook on Transit-Supportive Roadway Strategies • NCHRP Report 812: Signal Timing Manual, 2nd Edition (Urbanik et al.
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Traffic Control Strategy Toolbox 77 Benefits Bus delay will be reduced, as will the delay experienced by other vehicles sharing the intersection approach. The amount of time saved will be site-specific, but average movement delay reductions in the range of 10 to 30 s have been reported in the literature (e.g., Corey et al.
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From page 78... ...
78 A Guidebook on Transit-Supportive Roadway Strategies 6.6 Traffic Signal Shadowing Description A bus wishing to turn left at an unsignalized intersection triggers a call for a left-turn phase at a nearby downstream intersection, thereby creating a gap in traffic that the bus can use to turn left. Purpose When opposing traffic volumes are sufficiently high, and rightturning traffic from driveways or the downstream cross street fill available gaps before a bus can use them, buses may experience significant delays waiting to turn left at an unsignalized location.
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From page 79... ...
Traffic Control Strategy Toolbox 79 Benefits The delay benefit to buses is site-specific and would need to be determined from a traffic engineering study. Cost Considerations • Planning and coordination costs.
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80 A Guidebook on Transit-Supportive Roadway Strategies • Other user costs. Delay may be increased for traffic from the opposite direction if no leftturning vehicles would have needed to be served or when the left-turn phase is served earlier than normal.
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From page 81... ...
Traffic Control Strategy Toolbox 81 a provision for traffic signals required by buses was being considered for inclusion in a future edition of the MUTCD. Additional Resources • Manual on Uniform Traffic Control Devices (FHWA 2009)
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82 A Guidebook on Transit-Supportive Roadway Strategies Two key aspects of each of these TSP applications are that (1) signal timing changes are made within the context of the normal signal timing plan, and (2)
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Traffic Control Strategy Toolbox 83 • Timing transition. Changes to the signal timing are implemented to serve the request as soon as safely and operationally feasible.
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84 A Guidebook on Transit-Supportive Roadway Strategies in some cases the bus will simply arrive early at the next traffic signal and wait (see Section 4.4)
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Traffic Control Strategy Toolbox 85 The reasons why TSP does not always provide travel time benefits have not been well-quantified to date, but potential reasons include: • Too few priority calls, whether due to too-restrictive conditions (e.g., high thresholds for being behind schedule) or incorrect programming of the priority logic in the signal controller; • No change made to bus schedules to take advantage of potentially faster travel times, thus locking the scheduled travel time in place but reducing the number of late buses; • Locations for detecting the bus located inappropriately for the selected TSP application (e.g., providing priority for buses still serving passengers at a near-side stop)
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86 A Guidebook on Transit-Supportive Roadway Strategies Implementation Guidance As discussed in the Benefits section, TSP does not always provide a significant corridor-level travel time benefit. There it is suggested that the transit agency first investigate lower-cost, quicker-to-implement strategies that may provide as great or greater benefits than TSP.
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Traffic Control Strategy Toolbox 87 • Adjust the schedule to take advantage of any time savings provided by TSP; otherwise, giving priority only to late buses will lock the existing bus travel time in place. In this respect, TSP is well-suited for routes with headway-based schedules since conditional TSP can be configured to maintain bus headways while still providing a speed benefit.
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88 A Guidebook on Transit-Supportive Roadway Strategies Companion Strategies Transit signal faces are used to support other strategies that involve giving buses a head start on other traffic or moving from potentially unexpected locations. These strategies include bus-only signal phases (Section 6.9)
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Traffic Control Strategy Toolbox 89 Additional Resources • Manual on Uniform Traffic Control Devices (FHWA 2009) -- Section 4D.27 addresses the use of light rail transit (LRT)
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90 A Guidebook on Transit-Supportive Roadway Strategies operation of a bus-only signal phase used to allow buses to make a left turn from a right-side bus lane. Companion Strategies The need for transit signal faces (Section 6.8)
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Traffic Control Strategy Toolbox 91 Implementation Examples • San Francisco, California. A bus-only signal phase was used to allow buses to make a right turn from a left-side bus lane on a one-way street.
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92 A Guidebook on Transit-Supportive Roadway Strategies near-side bus stop, an over-capacity left-turn movement) where it would be desirable to allow buses to make a left turn from a right-side bus lane.
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Traffic Control Strategy Toolbox 93 stop; therefore, to avoid the potential for buses stopping twice (and needing to wait an extra cycle length) , bus stops should be either located at the far side or prior to the start of the rightturn lane.
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94 A Guidebook on Transit-Supportive Roadway Strategies in front of the bus to clear out of the way so the bus can proceed into the intersection. In step 3, the bus has cleared the intersection, and parallel traffic and the parallel crosswalk phases are served.
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Traffic Control Strategy Toolbox 95 (Section 6.5) , and transit signal priority (Section 6.7)
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96 A Guidebook on Transit-Supportive Roadway Strategies Another potential constraint is the ability to provide sufficient time during the traffic signal cycle to the queue jump, particularly in the case of shared right-turn lanes. The potential benefit of queue jumps grows as traffic volumes increase, but the ability to reallocate time within the signal cycle diminishes.
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Traffic Control Strategy Toolbox 97 the public (about queue jump operation generally) is suggested the first time a queue jump is implemented in a jurisdiction.
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98 A Guidebook on Transit-Supportive Roadway Strategies Far-side stops also work best in conjunction with short bus lanes or shoulder lanes and eliminate the requirement for a special queue jump phase since buses do not need to merge back into traffic immediately. Far-side stops can be used in conjunction with shared right-turn lanes but may not provide any operational benefit or may even provide a disbenefit.
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From page 99... ...
Traffic Control Strategy Toolbox 99 the bus to use the through lane to access the far-side bus stop. It can also be used with nearside stops if one is willing to accept that the bus will often stop twice when accessing the stop.
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100 A Guidebook on Transit-Supportive Roadway Strategies There are three main applications of pre-signals: • Virtual bus lane. In this application (Figure 8)
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Traffic Control Strategy Toolbox 101 • Weave assist. In this application, buses need to exit a bus lane to turn left at a downstream intersection.
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102 A Guidebook on Transit-Supportive Roadway Strategies (Hodge et al.
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Traffic Control Strategy Toolbox 103 • If the bus lane is restarted downstream of the intersection, the right lane will operate as an auxiliary through lane and will likely not be fully utilized. Procedures in NCHRP Report 707: Guidelines on the Use of Auxiliary Through Lanes at Signalized Intersections (Nevers et al.
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104 A Guidebook on Transit-Supportive Roadway Strategies virtual bus lane application. The pre-signal timing should allow vehicles to progress through to the main intersection without forcing traffic to stop twice.
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Traffic Control Strategy Toolbox 105 countries, signs exempting bicycles from the traffic signal indications would be inconsistent with the meaning of traffic signal indications provided in the MUTCD. Use with Transit Signal Priority In many of the installations documented in the literature, pre-signals have been combined with forms of TSP at both the pre-signal and the intersection.
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106 A Guidebook on Transit-Supportive Roadway Strategies At the time of writing, the MUTCD did not provide a traffic signal warrant specifically for bus operations. However, some of the MUTCD's signal warrants not related to traffic volumes may be applicable to the intersection and could potentially be used to justify a traffic signal that would also benefit bus operations.
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From page 107... ...
Traffic Control Strategy Toolbox 107 A third potential constraint is the possible effect of a new signal on roadway safety.
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From page 108... ...
108 A Guidebook on Transit-Supportive Roadway Strategies MUTCD warrants, an experimentation request would need to be prepared and approved by the FHWA to allow its use in the United States until such time that the MUTCD permits the use of signals specifically for buses. Note that a standard FHWA condition of approval is that the jurisdiction agrees to remove the installation (in this case, the signal)
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From page 109... ...
Traffic Control Strategy Toolbox 109 Constraints Enforcing traffic laws that affect bus operations may be a lower priority for the local police department than enforcing laws that affect traffic safety or addressing community crime issues. State and local laws may need to be changed to permit the use of photo or video enforcement for transit-related purposes.
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From page 110... ...
110 A Guidebook on Transit-Supportive Roadway Strategies installed cameras at 20 locations on three bus routes. Between April 2011 and March 2012, the cameras, in total, recorded approximately 6,000 bus lane moving violations per month, of which 14% were challenged, with 17% of the challenges being upheld, which is equivalent to 2% of all violation notices issued.
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