Dynamic turn restrictions can improve safety and efficiency at intersections with unconventional layouts, right-turn overlaps, emergency vehicle conflict concerns, and high pedestrian volumes.

Experiences in Overland Park, Kansas and Bellevue, Washington support the benefits of dynamic turn restrictions for improving safety and efficiency under specific circumstances.

Identifier
2016-B01104
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NCHRP Synthesis 447: Active Traffic Management for Arterials

Summary Information

This synthesis documents the state of the practice associated with designing, implementing, and operating active traffic management (ATM) on arterials. Information for this synthesis was gathered through a literature review of advanced ATM methods for arterials and in-depth telephone interviews of agencies selected through a screening interview. The study has provided information on strategies used to actively manage traffic and congestion on arterials; situations and operating conditions in which ATM strategies have been successfully and unsuccessfully deployed on arterials; and system and technology requirements associated with implementing the strategies.

Dynamic Turn Restrictions

Overland Park, Kansas uses dynamic turn restrictions for right turns at six locations to address three scenarios: intersections with recently removed right-turn overlaps, intersections that had unconventional layouts, and locations with fire truck conflict concerns.

The dynamic turn restrictions are implemented through the deployment of blank-out signs that illuminate when the right-turn-on-red is prohibited. The signs are straightforward to install: needing only to be placed in the correct location and connected to the proper terminals in the signal controller cabinet. While the signs cost more than static no-right-turn-on-red signs, the operational and safety improvements justified the additional cost. Additionally, the police approved the use of the signs and there were no issues with the city's municipal code.

Overland Park has found the dynamic no-right-turn-on-red signs provide increased safety by making right-turn-on-red restrictions more visible. The dynamic signs also provide improved operations because they do not have to restrict right turns at all times. Restrictions are in effect only when they are most needed. Furthermore, once the signs were deployed the city received requests from residents for the signs to be installed in additional locations.

Bellevue, Washington implemented a variable turn restriction controlling two signs restricting the eastbound right turn movement at NE 8th Street and Bellevue Way. The eastbound movement at this location has dual left-turn lanes, a through lane, and a shared through and right-turn lane and is the main exit route from Bellevue Square (a shopping mall). Bellevue Square has grown to occupy property adjacent to three quadrants of this intersection. The mall developer and city of Bellevue established agreements to allow pedestrian bridges between the buildings and parking garages on the east side of Bellevue Way. However, pedestrian traffic is still heavy across all legs of this intersection. Because of the high pedestrian traffic, essentially blocking any EBRT vehicles, eastbound capacity can be reduced by 50%.

Actuation of the turn restriction is based on occupancy data received from an upstream loop detector on the eastbound movement. A blank-out sign at the intersection is used to illuminate the traditional R3-1 sign. There is also an advance sign over the curb lane that can display two states: a through/right arrow and a through arrow only.

The adaptive signal system’s variation routines are used to test for cycle length and degree of saturation/occupancy on the eastbound advanced loop detector. In addition, timers have been implemented to ensure the turn restriction stays in the same state for at least 10 minutes to avoid the potential for on/off cycling. There is also a manual switch so police officers can manually turn the restriction on or off. Police are often used at this location for nearby festivals or big events, and the manual switch is useful to them.

Outcomes

In Overland Park, dynamic turn restrictions have proven effective in eliminating right-turn conflicts for the three situations for which the signs were placed. Safety improved at these intersections, and the signs allowed improved efficiency of the intersection because the prohibition was in effect only during conflicting left-turn phases.

The turn restriction strategy in Bellevue, Washington has generally increased capacity but the compliance rate is low. The compliance rate is higher when there are heavy pedestrian volumes. A prolonged police enforcement period increased compliance, which quickly decreased again after the enforcement period ended. Since implementation of the adaptive system with automated turn restriction, the number of calls to the city to request more time for eastbound traffic to exit their parking garages onto NE 8th Street has dropped from four to six per month to approximately four per year.

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Deployment Locations