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Suggested Citation:"Chapter 2 - Types of Systems." 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 2 - Types of Systems." 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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3At-grade intersections along busways can be classified into four types of intersections: (1) median busway intersections, (2) side-aligned busway intersections, (3) separated right-of- way intersections, and (4) bus-only ramps. (A given busway may have several of these types of intersections.) Each of these intersections is described in the following sections. Median Busways An exclusive busway that travels in the median of a road- way between opposing flows of vehicle traffic is classified as a median busway. The busway in Richmond, British Columbia, portions of the Orange Line in Los Angeles; and the busway under construction on Euclid Avenue in Cleveland are exam- ples of median busways in North America. Median busways are common throughout South America; Bogotá, Columbia, and Curitiba, Brazil, have noteworthy examples. Median busways generally have very wide intersections to accommodate both directions of general-purpose traffic, the busway lanes, and the median separation on one or both sides of the busway. They may also have platforms and left-turn lanes. Generally, a curb-to-curb envelope of 75 to 90 feet is needed to also accommodate left-turn lanes. When left turns can be prohibited, the cross section would be several feet shorter. If sufficient width exists near intersections and bus volumes are high, one or two extra lanes on the busway can be provided for express buses to pass local service buses. Busways are removed, both midblock and at intersections, from the curbside friction that may slow down operations; however, several safety and operations issues should be addressed. These issues include left-turn management, traffic signal placement, long pedestrian crossing distances, and pos- sible cross-street traffic queuing over the busway. Median busways conflict with the direction placement principle of traffic: buses travel straight through an intersection to the left of left-turning motor vehicle traffic, resulting in a direct con- flict between left-turning vehicles and same-direction transit vehicles. This conflict can be resolved through traffic controls that protect or prohibit left turns. However, the traffic control must be clearly separated for the two groups. Specifically, left- turning motorists should not be able to see the traffic control for buses, so that they are not confused about which control governs their movements at the intersection. Pedestrians and bicyclists should be channeled to desig- nated crossings at the intersections to discourage illegal cross- ing at other locations. Barriers or fences can potentially resolve midblock crossing concerns. Side-Aligned Busways An exclusive busway that travels parallel and closely spaced to an existing roadway, with some physical separation between the busway and general-purpose traffic is classified as a side-aligned busway. The maximum distance between the roadway and the busway, usually at the discretion of the designing agency, is likely to range from 100 to 400 feet. Inter- sections of side-aligned busways are so closely spaced to the intersections of the parallel roadway that they typically oper- ate together as one intersection. If the two intersections oper- ate independently, the busway is not side-aligned, but is instead considered separated right-of-way. A busway that is less than 100 feet from the general-purpose road results in a four-way street that can be confusing to motorists and pedes- trians. Examples include northern portions of the South Miami-Dade busway, the LYMMO busway in Orlando, and portions of the Orange Line in Los Angeles. A side-aligned busway intersection is very wide. Clear phys- ical separation between the parallel roadway, the side-aligned busway, and their intersections with the cross street is essential. A side-aligned busway is generally constructed along cor- ridors where the right-of-way is available. It consists of an exclusive two-lane roadway where each lane is reserved for one direction for buses to travel. If the right-of-way is suffi- cient, separation between the two directions should be C H A P T E R 2 Types of Systems

increased to provide an additional buffer between the buses and their mirrors. The main safety concern results from motorists on the par- allel roadway turning right across the busway and potentially into the path of an approaching bus. At intersections where the busway and parallel roadway have little separation, motorists are often prohibited from making right turns dur- ing the green signal phase for buses and must wait in a right- turn lane. At intersections with more separation, motorists turning right have to stop at the busway. Another concern with side-aligned busways is the potential for queues along the cross street to spill back over the busway. These concerns must be addressed by traffic control devices that reinforce the prohibition of vehicles blocking the busway. Separated Right-of-Way Busways Separated right-of-way busways operate on alignments independent of any parallel roadway: the busway is not in the median area and is not in proximity to a general-purpose road- way (i.e., it is at least 400 feet away; the actual distance depend- ing on the discretion of the agency). Examples include portions of the Ardmore busway in suburban Philadelphia, portions of the Orange Line in Los Angeles, and the southern portion of the South Miami-Dade Busway. At these locations, speed and motorist and pedestrian expectations are the primary concerns, especially where the intersections are not signalized. Intersections of separated right-of-way busways tend to be less wide than other types of busway intersections, because only the lanes for the buses are required. The intersection must accommodate the bus- way traffic, one or two directions of cross-street traffic, and pedestrian movements. Because of the sometimes light busway volumes (e.g., several minutes between buses), inter- secting motorists and crossing pedestrians may be inclined to overlook the possibility of vehicles approaching along the busway. Midblock pedestrian and bicycle crossings of busways are also classified as separated right-of-way busway intersections. Bus-Only Ramps For some systems, buses may have their own ramps to enter or exit the general traffic flow. The junction between the roadways and the ramps are also considered busway intersections. An example of this type of intersection is near the Airport Station of the Richmond 98 B-Line and along Pittsburgh’s South, East, and West busways. Discouraging and precluding illegal entry is the main reported concern with these intersections. 4

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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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