TxDOT Research Project

Guidelines for Applying Right-Turn Slip Lanes

Keeping on the Right Side of Safety
What Was the Need?
“Right-turn slip lanes” are pathways for right turns. If you’ve ever approached an intersection and seen a right-turn-only lane set off from the main lanes by a triangular concrete island, you’ve seen a right-turn slip lane. In separating the right-turning traffic, slip lanes reduce overall traffic delay and allow higher-speed right turns. Plus, those islands allow pedestrians to cross the road in two stages, which is safer. However, slip lanes can also encourage higher-than-intended speeds and create conflicts among cars, pedestrians, and bicyclists. TxDOT needed slip lane designs that balanced the safety and mobility of all roadway users.

What's the Solution?
To update TxDOT’s Roadway Design Manual with the most beneficial designs, CTR researchers thoroughly investigated various sources for the latest guidelines for right-turn slip lanes, and analyzed new designs already in use in other cities. The City of Ottawa’s “urban smart channel” design was a particular inspiration, because it incorporates a sharp angle of entry into the cross street (~70 degrees) and creates a narrow turning path for passenger cars using pavement markings, but is wide enough to accommodate larger vehicles, such as delivery trucks.

Research Benefits
CTR created design guidelines and standard drawings for TxDOT’s Roadway Design Manual, providing guidance for both new construction and retrofitting of right-turn slip lanes. In fact, this project’s findings were used to benefit actual traffic operations even before the project’s official end date—one of the primary researchers led a class for TxDOT staff at the October 2014 Short Course (a continuing education component of TxDOT).

Project Number
0-6810
Status
Completed

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Start Date
2/4/2014
End Date
10/31/2014
Performing Institution(s)
Center for Transportation Research (CTR)
Research Team
RS: Jennifer Duthie
Sponsor
Project Manager
Darrin Jensen
Page:
Index Terms
Channelized intersections
Crosswalks
Focus groups
Guidelines
Highway design
Highway safety
Literature reviews
Pedestrian safety
Right turn lanes
Lead University
CTR
Researcher
Duthie, Jennifer Clare
Bhat, Chandra R. (Chandrasekhar R. ), 1964-
Gemar, Mason

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"...As part of the ongoing I-35 improvements, DeGood studied the state’s Stassney Lane overpass project. With the inclusion of sidewalks and a bike lane, he said, the project is a 'multimodal win' by historical standards. Upon closer inspection, however, he noted that specific design elements indicate that 'the true purpose of the project is moving more cars and that cyclists and pedestrians are highly unlikely to use these elements with any meaningful frequency.' A major tell, he said, is the inclusion of slip lanes that allow vehicles to make right turns at higher speeds than would be possible at a 90-degree angle. This design, he explained, is 'intended to slingshot cars making right turns at high speeds, creating a severe safety risk for any pedestrian trying to walk through the corridor.' DeGood notes that, despite the inclusion of sidewalks and bike lanes, the state’s own “Guidelines for Applying Right-Turn Slip Lanes” [reports] acknowledge that these often increase speeds and create conflicts between motorists and those walking or riding bikes." --Thornton (2019 Dec 2) CAMPO 2040 plan, Stassney Lane overpass highlight common failures of multimodal projects. https://www.austinmonitor.com/stories/2019/12/campo-2040-plan-stassney-lane-overpass-highlight-common-failures-of-multimodal-projects/
4/24/2020 at 4:57 PM
0
Record Added:
11/25/2013
Record Updated:
6/1/2023 5:30 AM EDT

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