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Mid-America Transportation Center

NDOR Conditions Warranting Offset Right-Turn Lanes for Improved Intersection Sight Distance

Final Report
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Researchers

  • Principal Investigator: Karen Schurr (kschurr1@unl.edu 402-472-2233)
  • Project Status
    Complete
    Sponsors & Partners
  • Nebraska Department of Roads
  • About this Project
    Brief Project Description & Background
    Transportation agencies have started to use offset right-turn lanes (ORTLs) at two-way stop-controlled intersections in the hope of improving driver safety. An ORTL is similar to a standard right-turn lane except it has a painted or raised channelizing island that separates the right-turn lane from the through lanes. Still, offset right turn lanes require more right-of-way, more pavement, and more maintenance than an adjacent right turn lane. Research is needed to determine when construction of an offset auxiliary lane is cost effective. If an offset lane is required, design guidelines should be established that meet the goal of removing right-turning major road vehicles from the ISD triangle and meet driver expectations at these types of intersections.
    Research Objective
    The primary research objective is focused upon whether an SRTL or ORTL is the optimal choice at a given location where a right-turn lane is warranted along the major roadway of a two-way stopped-controlled intersection.
    Potential Benefits
    Since there are no standard guidelines used by the Nebraska Department of Roads for the appropriate three-dimensional intersection geometry to be used in creating an offset design, this research project provides recommendations for characteristics that should optimize function, operations and safety at such intersections.
    Abstract
    This project describes how right-turn deceleration lanes are auxiliary lanes built to decrease rear-end accidents near intersections along high-speed roadways and enhance through traffic operations by removing decelerating vehicles from the through traffic stream. However, at intersections with minor roads that have stop control or right-turn-on-red permission at signals, vehicles within the major road right-turn deceleration lane can inhibit intersection sight distance (ISD) by blocking the view of entering minor road drivers to oncoming through traffic. A solution for the minor road stopped driver is to wait until the sight triangle is clear of vehicles before attempting a left-turning movement. However, anecdotal evidence suggests drivers may become impatient or not realize that right-turning vehicles are significantly obstructing their vision. They may enter the major road without an appropriate gap in the traffic stream resulting in a right angle impact with an oncoming through vehicle which can cause severe injury to the vehicle occupants. The right turn lane obstruction can also prevent the approaching major road through driver from reacting defensively to an entering minor road driver accepting an unsuitable gap. Obviously, the proposed offset right turn lane design shown in the examples requires more right-of-way, more pavement, and more maintenance than an adjacent right turn lane. Research is needed to determine when construction of an offset auxiliary lane is cost effective. If an offset lane is required, design guidelines should be established that meet the goal of removing right-turning major road vehicles from the ISD triangle and meet driver expectations at these types of intersections.
    Project Amount
    $ 82,323