The National Academies

TCRP A-10A [Completed]

An Evaluation of Bus Bulbs on Transit, Traffic, and Pedestrian Operations

  Project Data
Funds: $175,000
Research Agency: Texas Transportation institute
Principal Investigator: Dr. Kay Fitzpatrick
Effective Date: 2/27/1998
Completion Date: 8/30/2000

During the 1970s, curb extensions, commonly known as bus bulbs, were built at bus stops along several downtown sidewalks in San Francisco as part of a transit preferential street program. The intent of the project was to allow buses to load and unload without pulling out of the traffic stream, thereby improving transit vehicle flow. In addition, the bus bulbs provided additional space to place pedestrian amenities in limited environments, such as sidewalks in dense urban settings. Benches were provided to give people places to sit away from the activity of the nearby sidewalk and stores, and transit shelters were moved onto the bulbs, which created additional sidewalk space for pedestrian circulation.

In the past, transit vehicles were observed stopping in the traffic lane, rather than pulling up to the curbside stop in the parking lane to avoid having to maneuver back into the stream of traffic. However, this type of informal strategy created hazards for pedestrians by making them walk over the curb and onto the street, which is especially difficult for the physically impaired. The bus bulbs provide enough space for bus patrons to comfortably board and alight the buses with little or no conflict from general pedestrian traffic.

From a traffic standpoint, bus bulbs limit the weaving movements the bus makes by having the bus remain in the flow of traffic while it dwells at a stop location, rather than pulling into and out of the curb side stop that is located in the parking lane. A trade-off, however, may be the formation of queues behind the stopped bus.

The city of San Francisco constructed bus bulbs at four sites at the intersection of Castro Street and 17th and 18th Streets. The sites were previously configured as curbside stops within a parking lane in a thriving and dense shopping and residential area. The bus bulbs were constructed to enhance transit operations in an area that experiences high vehicular volumes as well as high bus patron volumes. Existing sidewalks were limited because of the high pedestrian volumes and the dense urban setting. It was hoped that the additional space that bulbs provide would also give bus patrons adequate waiting areas.

The research studied the impacts that the bus bulbs had on traffic, nearby pedestrian movements, and transit operations at the sites in San Francisco. To accomplish this, data was gathered at the sites before and after construction to provide a comparative analysis between curbside stops in parking lanes and bus bulbs. The research team collected traffic data on vehicular volumes, travel times, queues behind the buses, weaving behavior of traffic behind the bus, turning movements at the nearby intersections, dwell times, and bus arrival/departure times. Pedestrian information was also gathered by mapping movement through the site, noting conflict points, and making field observations about changes in site utilization. In addition to the collection of field data, traffic performance at the bus bulbs was also evaluated using simulation.

Status: The final report and Appendix A have been published as TCRP Report 65. Appendices B, C, and D are posted below as Web Document 19. These documents are available in portable document format (PDF). (A free copy of Adobe Acrobat Reader is available at https://www.adobe.com.) Double-click on the links below to access the documents.

TCRP Report 65 - Part A
TCRP Report 65 - Part B
TCRP Report 65 - Part C

TCRP Web Document 19 Part A
TCRP Web Document 19 Part B

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