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Design, Operation, and Safety of At-Grade Crossings of Exclusive Busways (2007)

Chapter: Chapter 3 - General Principles of Safety and Design

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Suggested Citation:"Chapter 3 - General Principles of Safety and Design." National Academies of Sciences, Engineering, and Medicine. 2007. Design, Operation, and Safety of At-Grade Crossings of Exclusive Busways. Washington, DC: The National Academies Press. doi: 10.17226/23171.
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Suggested Citation:"Chapter 3 - General Principles of Safety and Design." National Academies of Sciences, Engineering, and Medicine. 2007. Design, Operation, and Safety of At-Grade Crossings of Exclusive Busways. Washington, DC: The National Academies Press. doi: 10.17226/23171.
×
Page 6
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Suggested Citation:"Chapter 3 - General Principles of Safety and Design." National Academies of Sciences, Engineering, and Medicine. 2007. Design, Operation, and Safety of At-Grade Crossings of Exclusive Busways. Washington, DC: The National Academies Press. doi: 10.17226/23171.
×
Page 7
Page 8
Suggested Citation:"Chapter 3 - General Principles of Safety and Design." National Academies of Sciences, Engineering, and Medicine. 2007. Design, Operation, and Safety of At-Grade Crossings of Exclusive Busways. Washington, DC: The National Academies Press. doi: 10.17226/23171.
×
Page 8

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5Busway intersections should provide safe and efficient movement of buses, general traffic, pedestrians, bicyclists, and other non-motorized users. Busway design should adapt and build upon the criteria and guidelines set forth in AASHTO’s A Policy on Geometric Design of Highways and Streets (1), ITE’s Traffic Engineering Handbook (2), and vari- ous Transportation Research Board publications. Busway intersection design also must consider several unique aspects of busway operations: (1) buses often operate at less frequent intervals (relative to motor vehicles); (2) bus- ways located near or adjacent to parallel streets increase motorist and pedestrian conflicts and confusion and can complicate traffic signal sequences; and (3) buses operating within arterial street medians may result in additional turning-movement conflicts and longer walking distances for pedestrians. This chapter presents general safety and design considera- tions that are particularly relevant for intersections of exclu- sive busways. Overview of Key Safety Issues at Busway Intersections Signal and Stop Sign Violation At all intersections, not just busway intersections, poten- tial violation of traffic control devices is a serious safety concern. At signal-controlled intersections, drivers who violate the traffic signal, namely the red signal indication, pose a safety hazard to other users of the intersection. Sim- ilarly, at stop-controlled intersections, vehicles failing to stop at the intersection pose a safety hazard to themselves and other users of the intersection. At busways intersec- tions, these violations can pose an even greater threat because of the difference in the size of the vehicles using the intersection. Understanding Traffic Control Devices Busway intersections can be new and confusing environ- ments to some users and, if users are unclear about the mean- ing of traffic control devices, particularly traffic signals, safety concerns can develop. If traffic signals are not appropriately designed and installed, motorists may confuse the meaning of the signal indications. Violation of Turn-Movement Prohibition At some busway intersections, turn movements may need to be prohibited either completely or during certain intervals, for example, right turn on red at side-aligned busway inter- sections. For intersections where the busway and parallel street are in proximity, right turns on red are prohibited so that vehicles do not turn into the path of buses on the busway. Violations of these turn prohibitions can present serious safety concerns. The prohibition should be clearly conveyed to motorists. Pedestrian and Bicycle Considerations Busway intersection users include bus operators, motorists, pedestrians, bicyclists, and other motorized users. Pedestrians and bicycles are vulnerable road users; their protection should be considered at all busway intersections. Pedestrians and bicyclists are less predictable than motorists in their movements. They are also less visible than vehicles, particularly at night. Bus operators must be trained to anticipate that pedestrians may cross against signals, out- side of crosswalks, and/or in front of buses. Busway intersections and designated midblock pedestrian crossings must be designed and operated to facilitate the safe crossing of these users. The safety of pedestrians with impair- ments also should be considered. For example, audible signals C H A P T E R 3 General Principles of Safety and Design

may be provided for pedestrians with visual impairments, particularly at signalized midblock pedestrian crossings that may lack some of the auditory cues (e.g., the sound “wall” of cross-street traffic) present at traditional intersections. Placement of Intersections and User Expectancy Drivers approaching an intersection rely on visual cues and/or experience to alert them to the presence of intersec- tions. The visual cues are necessary so that the driver can make the appropriate action at the intersection or react to others’ actions. Similarly, non-motorized users such as pedes- trians and bicyclists must have cues that they are approaching an intersection. Some of these cues may include non-visual cues, such as traffic noise. User actions at intersections include stopping for a traffic control device, checking for conflicting traffic, turning, and yielding to other intersection users, to name a few. For an intersection to operate safely and efficiently, all intersection users must act and react appropriately, based on a clear understanding of the actions to be taken. Busway intersections, particularly separated right-of-way intersections, may lack some of the visual cues normally used by drivers to detect the presence of an intersection. Because busways are not available roadways for general-purpose traffic and may be narrower than crossing roadways, drivers may assign busway intersections lower status and may not realize that the intersections exist. This problem is particu- larly an issue for relatively low-volume busways. If drivers often pass an intersection without having to stop, they may expect that they will never have to stop. Unauthorized Entry Unauthorized entry onto a busway, both intentional and unintentional, poses a serious safety risk to users—motorists may turn into the path of an oncoming bus. Appropriate measures should be taken both to alert motorists to the haz- ards of entering the busway and to provide positive guidance to vehicles traveling through intersections to minimize unin- tentional entry. Conflict Points at Intersections The number of conflict points at an intersection is related to the number of conflicting movements at the intersection includ- ing vehicle movements, bus movements, and pedestrian move- ments. Many busway intersections have more movements than traditional intersections. Figure 3-1 illustrates the 32 vehicle- to-vehicle conflict points (8 merge points, 8 diverge points, and 16 crossing points) at a traditional, four-leg intersection. The number of conflict points increases substantially as the number of legs increase. A three-leg intersection has 9 conflict points; a four-leg intersection has 32; and a five-leg intersection has 79. Similarly, adding a busway movement to an intersection increases the number of conflict points. A side-aligned busway intersection has four or more additional conflict points, depending on the separation dis- tance. Median arterial busway intersections have an addi- tional 12 vehicle-to-vehicle conflict points. The number of conflict points is even higher if turns are allowed into or out of the busway. Pedestrian conflict points, which are not included, can increase the number of conflict points by five or more per leg. Removing buses from general-purpose lanes to a busway eliminates all of the non-intersection conflict points and some of the intersection conflict points that buses traveling in the general-purpose lanes experience. For example, a bus traveling in the general-purpose lanes has to make a number of merge and diverge movements at bus stops. A bus along the busway does not have these conflict points. This reduction in conflict points improves safety for the buses and for passen- gers boarding and alighting. Design Principles and Guidelines Provide Simple Intersection Designs Busway intersections can be confusing to users because of the number of movements. Simple designs will help to minimize this confusion. Some basic design considerations include the angle of the intersection and the number of intersection legs. Right-angle intersections should be 6 Source: Signalized Intersections: Informational Guide (3). Figure 3-1. Conflict points at a traditional intersection.

encouraged for best sight distance. Crossings with angles of less than 75 degrees should be limited to merging and diverging movements. The number of intersecting intersection legs should be kept to a minimum. Intersections with more than four legs should be avoided. As discussed previously, the number of conflicts increases geometrically with the number of inter- section legs. Provide Clear Visual Cues to Make Busway Intersections Conspicuous As discussed in the overview of key safety considerations, the conspicuity (visual cues) of the busway intersection is important. Users approaching an intersection normally rely on visual cues to enable them to act or react to traffic control devices or other users appropriately. Pedestrians and bicy- clists also must have visual cues as they approach intersec- tions. Roadway designs and traffic controls should make busway intersections conspicuous to all users. Conspicuity can be achieved in several ways. The foremost visual cues are usually provided by traffic control devices such as stop signs or traffic signals. The Manual on Uniform Traffic Control Devices (MUTCD) gives guidelines for their appro- priate placement so they are visible to approaching motorists and pedestrians. Other visual cues include the cross-street pavement, mov- ing or waiting cross-street traffic, pedestrian signals, curbs and gutters at corners of intersections, crosswalks and other pavement markings, street name signs, splitter islands on the approach to intersections, turn bays, and overhead lane assignment signals. These cues, while sometimes lacking at busway intersections, are desirable and should be provided to the maximum extent practical. Other measures that can be taken at busway intersections, particularly separated right-of- way busway intersections, include • Illuminating intersections to improve nighttime visibility; • Providing overhead flashing beacons at unsignalized locations; • Providing curbs and gutters on approaches to intersections; • Using contrasting pavement color for busways (e.g., red); • Using contrasting pavement texture along intersecting streets on busway approaches (e.g., concrete pavement or rumble strips); and • Pavement markings and signage on streets crossing the busway. The use of traffic control devices such as signs and sig- nals to increase conspicuity is addressed in more detail in Chapter 5. Maximize Driver and Pedestrian Expectancy Expectancy can be achieved by having consistent designs and placement of traffic control devices at successive inter- sections to the maximum extent possible. Busway intersec- tion geometry should be generally similar from location to location. Safe stopping and decision sight distance should be adequate where complex decisions are required. Traffic signal controls, placement, phasing, and timings should be generally consistent from location to location. Separate Conflicting Movements Conflicting movements should be either prohibited or separated in space, time, or both space and time. Conflict points can be separated by the use of traffic control devices such as signals to assign right-of-way, exclusive signal phases, channelized turn lanes, and raised medians and islands. For example, providing protected left-turn move- ments instead of permitted left-turn movements separates in time the left-turning movement from conflicting move- ments such as opposing through traffic, busway traffic, or pedestrian movements. Alternatively, left-turn movements could be prohibited at the intersection to avoid the conflict altogether. Turns into and out of busway intersections for buses should be strongly discouraged. Prohibiting buses from mak- ing turns at busway intersections greatly reduces the number of conflicts involving buses, which is particularly important given their size, weight, and maneuverability. Minimize Street Crossings Overall, the best way to reduce conflicts with busways is to reduce the number of crossings of the busway. Crossings can be reduced by creating cul-de-sacs, requiring U-turns for minor streets, and spacing busway intersections widely. The spacing of intersections will depend on each area’s roadway configuration, local travel, and the importance of various streets in the surrounding roadway network. Sug- gested ranges for busway intersection spacing are presented in Table 3-1. 7 Surrounding Land Use Minimum Desirable Urban 1/8 mile 1/4 mile Suburban 5/8 mile 1/2 mile Rural 1/2 mile ≥ 1 mile Table 3-1. Suggested spacing for busway intersection by surrounding environment.

Incorporate Design Features that Improve Safety for Vulnerable Users Divider islands are used to separate busway lanes from adjacent travel lanes along median busways. However, they also provide refuge for pedestrians at intersections and should be designed with adequate dimensions for the expected pedestrian volumes. Many median busway intersec- tions will have very large crossing distances. Pedestrian refuges in medians and other dividers will help to facilitate safe crossings. The walking speed of pedestrians, particularly older pedestrians and pedestrians with mobility impair- ments, should be considered in the signal timing. Intersection designs should accommodate pedestrians with impairments, in accordance with the Americans with Disabilities Act, by (1) providing pedestrian ramps at inter- sections, (2) using contrasting pavement texture at critical locations such as truncated domes, and (3) using accessible pedestrian signals at appropriate locations. Coordinate Geometric Design Features and Traffic Control Devices The design and installation of traffic control devices such as signals, signs, pavement markings, and signage should be coordinated with the intersection geometry. Traffic signal placement and phasing should consider the needs of through, turning, and busway traffic. Where traditional signal displays are used for busway vehi- cles, these indications should not be visible to other movements. Visibility of these displays is particularly a concern for median busway and side-aligned busway intersections. Signs and pavement markings should be placed where the user can see the devices and have adequate time to react appropriately. Functional Analysis at Busway Intersections To provide a safe environment for all users of a busway intersection, the needs of those users must be understood. One method of identifying the needs of users is to conduct a functional analysis for the crossings. A functional analysis, also called a task analysis, identifies the information require- ments of each user, the source of that information, and the actions that are required of the user. From this information, inappropriate behaviors/actions can be anticipated and potential countermeasures can be identified to deter the inap- propriate actions. This method is based on an IDA (Information–Decision– Action) model, a simplistic human behavior analysis procedure used in the human factors arena to identify systematically the needs of a user in response to a given situation. This model takes on different elements for the specific task at hand. The primary application of this model in transportation is to iden- tify what information (e.g., signs, signals, pavement markings) a user needs to correctly decide how to maneuver through a transportation scenario (such as a busway crossing) safely. This approach is used in a number of similar applications including NCHRP Report 470: Traffic-Control Devices for Passive Railroad-Highway Grade Crossing (4) and NCHRP Report 130: Roadway Delineation Systems (5). Appendix H presents functional analyses for four intersec- tion designs: a median busway intersection, a side-aligned busway intersection, an independent (separate right-of-way) busway intersection, and a midblock pedestrian crossing. Many needs were identified in these functional analyses. However, the critical need of all users identified in these func- tional analyses was the need to know of the presence of the busway at the intersection. Chapter 5, Traffic Control Devices, provides suggested devices to provide this information to users. 8

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TRB’s Transit Cooperative Research Program (TCRP) Report 117: Design, Operation, and Safety of At-Grade Crossings of Exclusive Busways explores planning, designing, and operating various kinds of busways through roadway intersections. The report examines at-grade intersections along busways within arterial street medians; physically separated, side-aligned busways; busways on separate rights-of-way; and bus-only ramps. The intersections highlighted include highway intersections, midblock pedestrian crossings, and bicycle crossings. Appendixes A through I of the contractor’s final report were published as TCRP Web-Only Document 36.

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