APPLICATION & CONTEXT
Turn restrictions may be applied on streets with or without dedicated transit lanes.
Left-turn restrictions are broadly applicable to multi-lane two-way streets, and may be beneficial on two-way streets with one lane per direction with very high transit volumes.
Left-turn prohibitions are an important component of high-capacity center-running transit services, such as center-running BRT and LRT. Streets with BRT and LRT should prohibit left turns from the transit lane, permitting them only from an adjacent lane with a dedicated turn phase.
Right-turn prohibitions are especially useful for intersections in downtown areas with high walking and bicycling levels, or for streets with right-side bike facilities, where permitting turns would result in long delays for transit vehicles running in the right lane.
Turn management is required for side transitways.
Bicycle turns have minimal impact on transit and pedestrian traffic, and can be permitted even where other turns are prohibited.
Left-turn restrictions may substantially reduce transit delays for all types of transit facilities except one-way street right-side facilities.
Left-turn restrictions may reduce the frequency of pedestrian injuries and the frequency of transit-involved motor vehicle crashes.
In New York, left-turn crashes involving severe pedestrian injuries outnumbered right-turn crashes 3 to 1. Additionally, pedestrians struck crossing at signals had the signal in 57% of cases.
Rob Viola, Matthew Roe, and Hyeon-Shic Shin. The New York City Pedestrian Safety Study & Action Plan. New York City Department of Transportation (2010).
Right-turn restrictions for curbside and offset transit lanes prevent transit delays from turning vehicles and may reduce the frequency of pedestrian injuries.
On two-way streets, left-turn restrictions can substantially increase the capacity of general-traffic lanes. In streets operating at or near capacity, this may enable the implementation of a transit lane while minimizing delays and queuing for general motor vehicle traffic.
Where the turn to be prohibited has a moderate or high existing traffic volume, diversion is likely to occur. Alternate routes for the turn should be identified that would generate fewer conflicts between turning vehicles and pedestrians, transit service, and oncoming traffic.
Consider network connectivity when planning turn restrictions. Network analysis should at minimum identify alternate paths for vehicles to access the specific block that would no longer receive a turn, considering the availability of turn pockets, general intersection geometry, walking and biking volumes, and other aspects of turns. Some diversion paths may be less desirable than the original turn, while others can be safer and more efficient with relatively simple interventions.
Left-turn prohibitions may improve operations for right-side running transit operating in mixed-traffic lanes. However, right-turn volume increases must be accounted for when considering potential benefits for transit operations.