Improve Sight Distance at Signalized Ramp Terminals of Partial-Cloverleaf Interchanges to Deter Wrong-Way Entries

Abstract

Providing drivers with open sight distance on entrance ramps can help prevent wrong-way entries at interchange terminals. For partial-cloverleaf (parclo) interchange terminals with close-spaced two-way ramps, appropriate intersection balance and median barrier lengths can provide motorists with a better view of entrance ramps and a better turning radius. A current best intersection balance practice by Washington State Department of Transportation (WSDOT) is to locate the stop line at no more than 60% of the way through the intersection. However, this has not been proven for safety benefits. To fill this void, this paper provides a comprehensive evaluation of the impact of stop line positioning based on wrong-way crash data analysis. Effects of different lengths of the median barriers used to separate two-way ramps on left-turn driver sight distances were also investigated by analyzing driver perspectives of roadway information with a three-dimensional (3D) simulation and analytical methodology. Conclusively, the current best practice was proven effective in deterring wrong-way driving, and general guidelines for appropriate median barrier lengths on two-way ramps were developed.