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Section 3: Retrofitting Treatments

Common issues encountered at right-turn slip lanes include the absence of adequate refuge in the channelizing island for crossing pedestrians, failure of motorists to yield to crossing pedestrians, pedestrian noncompliance with the crosswalk location, high-speed turns jeopardizing pedestrian safety, low visibility of crossing pedestrians, and excessive head turning required to observe oncoming traffic. These observations should be supported by collision diagrams and/or crash analyses of the intersection. Potential retrofitting treatments designed to mitigate these issues are presented below.

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Providing Proper Refuge for Pedestrians

Where the channelizing island along a right-turn slip lane is painted and does not provide adequate refuge for crossing pedestrians, consideration should be given to installing a raised island. Raised pedestrian islands reduce the crossing distance for pedestrians by allowing pedestrians to cross the through lanes and turning roadway separately while taking refuge on the island between. The reduction in crossing distance may also improve signal timing.

At intersections where there is a raised channelizing island but it is not large enough to provide refuge for pedestrians, the island should be expanded to establish an adequate landing area for pedestrians and comply with ADA regulations. The minimum recommended size of the channelizing island is 300 ft2 for intersections in all area types; the specific site conditions will dictate the final size.

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Yielding to Crossing Pedestrians

At intersections where there is a concern that motorists are failing to yield to crossing pedestrians, several treatments to improve compliance can be considered. These treatments are intended to achieve one or both of the following: improve the visibility of the crosswalk, and decrease the speed of right-turning motorists. When visibility is a concern and the crossing is currently marked, consideration may be given to upgrading the crosswalk markings to include longitudinal bars and incorporate a “ladder” pattern. An advanced warning sign (W11-2) and yield stripe may also be installed (see Figure D-3).

In areas where pedestrian activity is moderate to high, raised crosswalks may be installed to slow turning motorists and improve their likelihood of yielding to crossing pedestrians. However, raised crosswalks are not recommended along high-speed facilities. Signs with pedestrian-actuated flashing beacons may be installed to provide an advanced warning to approaching motorists of the need to comply with the crossing location. Caution must be taken when installing beacons where pedestrian activity is minimal and the infrequent activation of these beacons may violate driver expectations.

NCHRP Report 562 provides additional guidance concerning different types of crossing treatments based on observed conditions, including thresholds for pedestrian and vehicle volumes and roadway speed5.

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Crosswalk Location

Crosswalks should be placed in the middle of the channelized roadway, perpendicular to the direction of traffic. Being the shortest path, this treatment is likely to increase compliance. Signs may be used to direct pedestrians to the location where they are expected to cross. The R9-2 sign (Figure D-6) is a regulatory sign for crossing pedestrians.

R9-2 Sign (TMUTCD) (click in image to see full-size image) Anchor: #VDYXCSBVgrtop

Figure D-6. R9-2 Sign (TMUTCD)

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Reducing Speeds in the Channelized Roadway

High-speed turns are generally promoted by wide, sweeping turning roadways and the presence of acceleration lanes downstream of the right-turn slip lane. When applicable, consideration should be given to striping turning roadways in order to delineate the path for passenger vehicles and promote a sharper entry angle with the cross street. Also, the presence of a deceleration lane upstream of the turning roadway provides an area for approaching vehicles to decrease speed before making the turn while separated from through traffic. Consideration for removing the acceleration lane where their presence is not necessary (mainly along urban and suburban streets) may be appropriate as they promote high-speed turns and may cause inconsistent driver behavior (e.g., some drivers may stop or slow to look for oncoming traffic before they proceed, while others continue at pace into the acceleration lane and look for a gap closer to the downstream merge location). See Figure D-4 for the recommended design configuration of a right-turn slip lane with a deceleration lane, including pavement markings.

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Enhancing Visibility of Crossing Pedestrians

At locations where the visibility of pedestrians is low, warning signs may be installed in advance of the crosswalk to alert motorists of the presence of a crosswalk ahead. Consideration should be given to striping the crosswalk with “ladder” markings to enhance the visibility of the crossing location. Provision of a deceleration lane upstream of the turning roadway better accommodates a decrease in speed by approaching motorists, which provides them more time to spot crossing pedestrians. Reconstructing the turning roadway and channelizing island to incorporate a more pedestrian-friendly design may be an option as part of intersection improvements. If intersection lighting is absent or insufficient, addition or enhancement of lighting to illuminate the crossing and surrounding area may be appropriate. Other potential treatments include rectangular rapid flashing beacons, or other pedestrian-actuated traffic control devices that alert motorists to the presence of the crossing location only when pedestrians are present. This not only improves the safety conditions at these intersections but actuation may reduce the impact to motorists’ mobility.

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Reducing Head Turning to Spot Oncoming Traffic

At intersections where motorists are required to turn their heads excessively to observe oncoming traffic, consideration should be given to reconfiguring the channelizing island and turning roadway such that the angle of entry is closer to 70 degrees. As a result, navigating the turning roadway does not require as much physical effort to observe cross street traffic. This may involve reconstructing the channelizing island/outside curb radius or restriping the island area and turning path.

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Slip Lane Removal

If none of the available right-turn slip lane treatments will address existing safety problems at the turning roadway, and pedestrian activity is very high, consideration may be made to close the slip lane and transform the area into a pedestrian-friendly corner with street furniture, benches, and landscaping. A shared through-right-turn lane would replace the slip lane to accommodate the right turning movement. However, this option should be carefully considered as the removal of the slip lane may eliminate a number of benefits, including the reduction of vehicular delays and rear-end crashes.

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