Countermeasures to Reduce Crashes at Signalized Intersections Near Vertical Curves

Project Description

Vertical curves close to traffic signals create the possibility that queued vehicles, or even the signal indications themselves, will be obscured or fully hidden by the roadway surface on the crest of the curve. Existing signing standards contained within the Texas Manual on Uniform Traffic Control Devices (TMUTCD) address this situation by providing specific locations for SIGNAL AHEAD signs when at least two signal indications cannot be seen a certain distance upstream from the signalized intersection. The TMUTCD also allows for the placement of supplementary advanced warning BE PREPARED TO STOP signs at locations which have SIGNAL AHEAD signs in the proscribed location. However, little guidance is provided on the proper location of the BE PREPARED TO STOP signing. This project examined the roadway environment and driver line of sight for situations where crest vertical curves are found on the approach to a signalized intersection. Researchers identified a segment of roadway along the approach where stopping sight distance is provided as per geometric design standards, but where extra sight distance, known as decision sight distance, was not provided, despite the fact that intersections require a driver to safely make decisions regarding vehicle speed and path. The researchers labeled this zone the reduced decision zone (RDZ) and provided easy-to-use nomographs to determine its location for a range of rural and urban design speeds and vertical curve grades. Researchers also used this information to produce signing nomographs for the location of BE PREPARED TO STOP supplemental advanced warning signing.

Project Publications

Improving Safety at Signalized Intersections near Vertical Curves 0-4084-1

Guidelines for the Use of Countermeasures to Reduce Crashes on Approaches to Signalized Intersections Near Vertical Curves 0-4084-P1

Guidelines for Using Decision Sight Distance at Signalized Intersections near Vertical Curves 0-4084-P2

Improving Driver Perception of Signals near Vertical Curves 0-4084-S

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