In Washington D.C., allowing transit vehicles priority during a no-notice evacuation resulted in a 26 percent time saving for transit buses without impacting on personal vehicle travel time.

Results from research testing the effects of transit signal priority on evacuation clearance times for transit and personal vehicles.

Date Posted

Utility of Transit Signal Priority For No-Notice Urban Emergency Evacuation

Summary Information

This research addressed the question of whether to allow transit vehicles priority during no-notice urban evacuations in which there is no police assistance at traffic controlled intersections. In certain emergency scenarios it may not be advisable or even possible to follow the standard practice of placing police officers at intersections throughout the evacuation area. Emergencies involving dangerous environmental factors such as the presence of fire, chemical plume, radioactive fallout (nuclear contaminated wind and dust) prohibit police presence. However, in such circumstances and particularly in high-density urban areas, there is a strong demand for transit vehicles to assist in the egress of the population.

This case study of a no-notice evacuation examined the impact of allowing transit signal priority on the evacuation clearance time of transit vehicles and personal vehicles.


The study area was a 14-intersection corridor located in the Southeast corner of Central Washington, DC (NW 7th Street from SW E Street (South) to NW Pennsylvania Ave, West to NW 12 Street). The corridor encompasses a major metro station in the city (L'Enfant Plaza), and is one of the 19 major corridors designated as a primary evacuation route to assist in the evacuation process. The scenario was the detonation of a dirty bomb at L'Enfant Plaza, setting in motion the city's emergency evacuation response.

The methodology used a microscopic traffic simulation of an evacuation environment merged with a transit operations and signal priority component. The evacuation environment consisted of socio-economic data, census data and regional evacuation data, and the transit operations and signal priority component was built from data on street geometry, signal timing data, traffic counts and transit information (schedule, stop location, dwell time, etc.). These models generated an evacuation origin destination (O-D) matrix to create a realistic emergency evacuation traffic model with measures of effectiveness (MOE’s) including travel time, evacuation clearance time, and delay time. The simulation network included 17 of the 34 bus lines within the borders of the study area. The bus lines not included were those that do not require priority (right hand turns only) or do not use more than one intersection within the study corridor.


Allowing transit signal priority during the evacuation resulted in a 26 percent time saving for transit buses, meaning that three prioritized vehicles accomplish the same as four would without priority. The 26 percent time savings enables more transit units to make additional trips, resulting in shorter evacuation times. The results also found that the time saving is achieved without having an impact on evacuation clearance times or evacuee travel times for non-transit vehicles. Moreover, when transit signal priority is restricted to operate only on evacuation routes, evacuee travel and delay time decreases (in contrast to previous studies that found transit priority results in delays to vehicular traffic during high roadway demand).

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