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

Chapter: Chapter 7 - Busway Intersection Design

« Previous: Chapter 6 - Operational Practices
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Suggested Citation:"Chapter 7 - Busway Intersection 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 7 - Busway Intersection 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 7 - Busway Intersection 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 7 - Busway Intersection 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 29
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Suggested Citation:"Chapter 7 - Busway Intersection 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 7 - Busway Intersection 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 31
Page 32
Suggested Citation:"Chapter 7 - Busway Intersection 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 32
Page 33
Suggested Citation:"Chapter 7 - Busway Intersection 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 33
Page 34
Suggested Citation:"Chapter 7 - Busway Intersection 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 34

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26 This chapter provides design guidelines for various busway intersections. These guidelines apply the basic principles and policies set forth in the previous chapters. As discussed in Chapter 2, there are four basic types of at-grade busway intersections: (1) median intersections, (2) side-aligned intersections, (3) separated right-of-way intersections, and (4) bus-only ramps. Each type of intersec- tion is described in the following sections. Median Busway Intersections Busways located in the median of a roadway are median busways. The busway is physically separated from the general- purpose traffic on both sides. This type of busway removes the buses from curbside conflicts. This design concept is widely used in South America. The 98 B-Line in Richmond, British Columbia, is an example of a median busway in North America. This design concept requires a curb-to-curb width of at least 80 feet, although wider cross sections are more desirable to accommodate turning movements and median separation. Safety Issues The median busway can increase the complexity of the inter- section. This type of intersection has a very wide crossing dis- tance for pedestrians. Pedestrian refuge should be provided in the median, particularly if there is a station at the intersection. Left turns are a concern at this type of intersection. Because of the proximity of the median busway to the left-turn lanes from the parallel roadway, left-turning motorists may confuse the bus signal with their own if standard signals are used. Also left turns from the cross street may inadvertently turn into the busway if the appropriate path guidance, usually pavement markings, is not provided. If the intersection is congested, these left-turning vehicles from the cross street may back up over the busway. Basic Geometry The intersection geometry must fully integrate transit operations and traffic control devices. The controlling design factor is the placement of arterial left-turn lanes and busway stops. There are generally three options for their placement: • Left-turn lanes on the near side and bus stops on the far side of the same intersection • Left-turn lanes and busway stops at separate intersections • Signalized indirect left turns (such as Michigan lefts or jug handles) with all left turns moved away from the busway intersection A busway can incorporate one or more of these options. In designing the intersection, the effect of the design on transit operations and traffic control devices must be considered. Physical separation between the busway and the general- purpose traffic by raised islands with mountable curbs is desirable. A minimum separation of 4 feet will provide space for signs and some refuge for pedestrians, although 6 feet or greater is preferred for pedestrian storage. When space is extremely limited, channelization such as flexible posts placed in predrilled holes, raised pavement buttons, or wide rumble strips can be used to provide the physical separation require- ments. Orlando’s LYMMO system uses double rows of raised pavement buttons. Bus stations should provide at least two loading positions (100 feet for regular buses and 140 to 150 feet for articu- lated buses). Stops may be located on the far side and should be at least 8 feet wide, although a 10-foot width is preferred. Pedestrian access should be at signalized locations only. Landscaping, fencing, and other devices should be used to channel pedestrians to cross at the intersection. The Euclid C H A P T E R 7 Busway Intersection Design

27 corridor median busway in Cleveland will use the platform height to channel pedestrians leaving the station to cross at the intersection. The platform will be raised 14 inches off the ground to deter pedestrians from leaving the station from the platform. Traffic Control Median busway intersections should always operate under signal control. This control is necessary to assign right-of-way to the multiple conflicting movements at the intersection, including pedestrian movements. White bar signals are preferred for busway control because motorists, particularly left-turning motorists, will be less likely to confuse them with parallel-roadway traffic signals. Example Intersection Figure 7-1 presents an example of a median busway inter- section. There are far-side stops for each direction. Left turns are allowed from the parallel roadway in a lagging, protected- only phase. The bus phase is concurrent with the parallel- roadway through phase. White bar signals are used to control the busway. Standard signals are used for roadway traffic. Selective-view program- mable lenses are used on the parallel roadway so that motorists do not mistake adjacent lane signals (i.e., left-turning motorists do not mistake the through-vehicle signals) for their own. This example intersection has separate right-turn bays for right turns from the parallel roadway. In many situations, the available right-of-way will be limited and the use of right- turn bays may not be practical with the available space. Please note that Figure 7-1 does not present a complete traffic control device plan. Side-Aligned Busway Intersections The intersections of a cross street and a busway located adjacent to a parallel roadway are called side-aligned busway intersections. Side-aligned busway intersections are typically Figure 7-1. Example of a median busway intersection.

28 located between 50 and 400 feet from the parallel roadway. The two intersections usually function together as one inter- section. Depending on the distance between the parallel road- way and the busway, vehicle storage may be allowed on the cross street between the two. Safety Issues This intersection design can be confusing to motorists who are unfamiliar with this type of intersection. Traffic control devices such as lane assignment signs, pavement markings, and traffic signal heads should be used prudently to assist the motorist. Visual clutter should be reduced. Right turns from the parallel street onto the cross street can conflict with the busway during the bus phase. If adequate storage is not available between the intersections, right turns on red should be prohibited.Violation of this prohibition can have serious safety consequences. Traffic queuing over the busway intersection from the parallel-street intersection is also a concern. The two intersec- tions must be coordinated so that vehicles do not wait for the parallel-street intersection over the busway. The busway and cross-street intersection must be equipped with traffic signals. Basic Geometry The geometry of the busway and the cross street is similar to the geometry for the separated right-of-way intersection. No turns from the cross street are allowed at this intersection. Turns may be allowed from the busway; however, the number of conflict points at the intersection will increase and, there- fore, turns should be limited or avoided all together if possi- ble. Along the parallel street, right- and left-turn lanes or bays are essential to provide a safe refuge area for vehicles to wait during the red phase. Both of these turns should operate in a protected phase. If these lanes are not provided, then the right and left turns from the parallel street onto the cross street that leads to the busway should be prohibited. Traffic Control Traffic signal control along the cross street at the busway and at the parallel street are the preferred control for this type of intersection. The signal phasing between the two intersec- tions should be coordinated to avoid vehicles queuing over the busway. Buses on the busway can move during the same phase as the parallel-street through movement. During this phase, the conflicting left turns from the parallel street should be pro- hibited. Conflicting right turns should be prohibited if stor- age between the two intersections is not adequate for the vehicles. A clearance phase should be provided for cross-street traffic before the busway phase when the distance between the busway and the parallel street is less than 200 feet. Example Intersection Figure 7-2 presents an example of a side-aligned busway intersection parallel to a major arterial. In this example, vehi- cle storage between the two intersections is not allowed. Therefore, right turns on red are prohibited from the arterial. The bus phase can be concurrent with the through-vehicle phase for the parallel arterial or a separate phase. Leading left turns are used. White bar signals are used to control the busway. Standard signals are used for vehicle traffic. The vehicle signals at the busway intersections use a green arrow for the through indi- cation to emphasize the turn prohibitions. All signals are equipped with back plates. Although not pictured in Figure 7-2, other traffic control devices such as busway crossing warning signs should be used. Please note that this figure does not present a complete traffic control device plan. Separated Right-of-Way Busway Intersections Separated right-of-way busway intersections are also referred to as isolated busway intersections. These intersec- tions are not situated close to other intersections or roadways. A two-way busway, potentially with passing lanes at the inter- section, intersects a cross street. The intersection is signalized or stop controlled. Safety Issues A few potential safety issues should be considered in the design of this type of busway intersection based on the reported experiences of agencies that use this design. The first issue is the recognition of the busway crossing as an intersection by motorists, pedestrians, and bicyclists. Users may not expect buses to cross from what may look like a sec- ondary street. The intersection should be highly visible and should be designed with the same elements as other intersec- tions (e.g., street name signing, curb and gutter, and stop bars). If the intersection is not visible, motorists may inad- vertently violate the traffic control devices. Similarly, if the intersection is not recognized as such, motorists will be more likely to violate the traffic control devices intentionally. The second issue is related to the type of intersection control devices at the intersection.The busway volumes may not be suf- ficient to warrant a traffic signal based on currently established warrants for signalization, which are based on vehicle volumes not person volumes. If stop control is used at the intersection, inappropriate gap acceptance may cause a safety concern.

Figure 7-2. Example of a side-aligned busway intersection.

30 Basic Geometry The basic geometry for this type of intersection is a two- lane busway intersecting a two- to four-lane roadway. If there is a stop at the intersection, the busway may have passing lanes at the station. Far-side stations are preferred with this design. Signalized Intersections Signal control is the preferred method of intersection con- trol, particularly if the cross street is a major street. White bar traffic signals are preferred for busway control, although sig- nals are not as important for this type of busway intersection because there are not any parallel vehicle movements. The use of semi-actuated controls or TSP for the busway will allow the busway a green phase on demand after the minimum green phase for the cross street. When the cross street is part of a coordinated system, the bus-actuated phase operates within established background cycles. Because traffic signal violations are a concern at this type of intersection, the use of 12-diameter signal displays with back plates is appropriate. Turns are not allowed at these intersections; therefore, a through green arrow, yellow ball, and red ball are the preferred signal displays. Pedestrian signals may be necessary where there are cross- walks. If the busway phase is actuated, pedestrian actuation is needed for the parallel pedestrian movement. Stop-Controlled Intersections Stop sign control for the cross street may be necessary at some low-volume intersections. If used, stop sign control should be used in combination with such strategies as stop-ahead signs, flashing beacons, and transverse rumble strips to reinforce the stop sign control and the presence of the intersection. The type of stop control (i.e., two-way or four-way) depends on the volume of the intersection and the available gaps. For transit speed and efficiency, it is preferable to stop the traffic on the cross street instead of the busway. However, in most cases, stopping the cross-street traffic without also stopping the busway traffic is not practical; the cross-street volumes are likely much higher than the busway volumes. Stop control on the busway increases the delay for the bus.Additionally, if only the busway is stop controlled, larger buses may find it difficult to locate a suit- able gap in cross-street traffic. Therefore, four-way stop control may be necessary to ensure safe operation of the intersection. Example Intersections Signal-Controlled Intersection Figure 7-3 presents an example of a signalized, separated right-of-way busway intersection. In this example, there are two far-side stations at the intersection, one for each direction. No turns are allowed at this intersection. Although not dis- played on this drawing, numerous signs (as discussed in the chapter on traffic control devices) would be used to commu- nicate this message to the motorist. White bar signals are used to control the busway approach. Standard signals are used for cross-street traffic. A green arrow is used for the through-vehicle indication. A two-phase signal is used to control traffic. Stop-Controlled Intersection Figure 7-4 presents a stop sign-controlled intersection. In this example, there are no stations at the intersection. The type of stop control at a separated right-of-way inter- section depends on the volume of the traffic at the intersec- tion and the best way to safely accommodate the intersection demand. Generally, four-way stop control is preferred. In this example, the intersection is controlled by two-way stop signs on the cross street and the busway is uncontrolled. Several traffic control devices can be used to reinforce the presence of the intersection and the traffic control for the cross- street traffic. In this example, graphic Stop Ahead warning signs are placed on the cross-street approaches. The intersection is also equipped with an overhead flashing beacon. The beacon flashes red for the cross-street approach and yellow for the busway approach. Other measures that can reinforce the stop control include transverse rumble strips, Stop Ahead pavement markings, and larger or double stop signs on the approach. Although not pictured in Figure 7-4, a busway warning is sug- gested for this intersection.The South Miami-Dade busway will use intersection islands on the approaches to increase the con- spicuity of separated right-of-way intersections. An example of such intersection islands is included as Figure 7-5. Bus-Only Ramp Intersections Ramps are an important component of an exclusive, fully separated busway system. They are used where busways begin, end, branch, or connect to the surrounding road system. Bus-only ramp types include connections from bus lanes located in freeway medians to bus terminals. Examples include the bus-only ramps in the San Francisco Bay area, the bus-only ramps from park-and-ride lots in Houston, and the bus-only ramps at the airport station in Richmond, British Columbia. Other bus ramps include connections from city streets to the beginning or end of the busway such as those used to connect to the Pittsburgh busway. General Guidelines Intersections of busway ramps and public roads are designed similar to other intersections. However, they require clear messages indicating that the ramps are only for bus use.

Figure 7-3. Example of a signalized, separated right-of-way busway intersection.

Figure 7-4. Example of a stop-controlled, separated right-of-way busway intersection.

33 Roadway geometry and traffic control devices, while similar to other intersections, should accommodate bus turning movements with minimum encroachment on opposing travel lanes. Ramps may be one way or two ways depending upon specific circumstances. Bus-only left-turn lanes should be provided on the cross streets. The lane should be designated for buses only by pave- ment markings and signs. Signing should be clear and should prohibit turns by general traffic. Dual Do Not Enter signs should be erected on the ramp entrance, with a supplemen- tary plaque that exempts transit vehicles. Both side-mounted and overhead signs can be used. Basic Geometry Intersection of the busway and the connecting ramps should be similar. Turning lanes should be provided where space permits to remove buses from the through travel lanes. Ramp design should provide adequate space to allow pass- ing around disabled buses. Such adequate space suggests a single-lane ramp with wide shoulders or a two-lane design. Single-lane ramps should be 12 to 14 feet wide, with 10-foot shoulders on both sides. Traffic Control Traffic signals should be considered for situations where traffic volumes along the entry are heavy and gaps are not suf- ficient. Semi-actuated traffic signals operating on the cross- street background cycles should be used. Effective enforcement of the prohibition of unauthorized entry to the busway ramp is essential to discourage errant drivers. Where violations persist, bus-activated gates may be needed. These gates should be placed across the ramp about 50 to 100 feet away from the intersection. Example Bus-Only Ramp Figure 7-6 presents an example of a bus-only ramp inter- section from NCHRP Report 155 (17). In the example, a bus- only left-turn lane is provided to enter the ramp. The intersection is uncontrolled. For low-speed, low-volume bus traffic, the offsets and even the left-turn lane could be omit- ted. Sufficient levels of illumination should be provided regardless of volume. The design in Figure 7-6 would be greatly improved by the use of Bus Only pavement markings at the entrance to the ramp. Figure 7-5. Example of stop-controlled, separated right-of-way busway intersection in South Miami Dade.

34 Source: NCHRP Report 155 (17). Figure 7-6. Example of a bus-only ramp intersection.

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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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