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

The research described herein documents an investigation into countermeasures that can be used to provide motorists with advance notification of traffic signals or queues from those signals that are located beyond the motorists' line of sight due to a vertical curve. A "reduced decision zone" (RDZ) was identified in the research as the location along a roadway with a vertical curve and a traffic signal beyond the curve where stopping sight distance (SSD) is provided but decision sight distance (DSD) is not. Essentially, motorists within the RDZ are provided with SSD for unexpected stopping but are not provided with the added decision-making and response time that DSD might otherwise provide as they approach the vertical curve and the downstream traffic signal. Contained within this report are techniques for determining whether an RDZ exists along an existing roadway. In cases where a traffic signal or queue from a signal is located within the RDZ, guidance is provided on both the type and location of countermeasures that can be used.