BENEFITS

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.

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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.

CONSIDERATIONS

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.

RECOMMENDED

Turn prohibition signs should be placed where they will be most easily seen by drivers who might be intending to turn. A NO RIGHT TURN sign should be installed adjacent to a signal face viewed by drivers in the right lane.

The NO LEFT TURN (or NO U-TURN or combination No U-Turn/No Left Turn: MUTCD R3-18) sign should be installed adjacent to a signal face viewed by road users in the left lane. A left-turn blank-out sign may be installed where left turns are prohibited while transit vehicles are present.

A NO TURNS sign should be placed adjacent to a signal face viewed by all road users on that approach, or two signs may be used (MUTCD §4D.34).

For bus lanes with turn restrictions, a solid lane line should be marked at the approach to the intersection along the bus lane.

If dedicated bicycle infrastructure is present on a street, bikes should be excepted from the turn restriction and provided with a short approach lane or other facility.

If turns can be made from a previous intersection, install wayfinding signage in advance of the prior intersection.

OPTIONAL

Wayfinding signage can be provided to direct vehicles to permitted turns or recommended diversion paths.

Vertical separation elements or other self-reinforcing geometric design elements may be installed to prevent or discourage prohibited turns.

Part-time turn prohibitions, usually applied during peak multi-modal traffic periods, are a useful tool for minimizing delays on streets without dedicated turn space. While peak-period left-turn prohibitions are a conventional strategy to increase general-traffic throughput—potentially resulting in higher traffic volumes over time—peak-period turn restrictions on left turns or right turns can substantially improve the performance and safety of either a peak-only transit lane or full-time transit lane.