Horizontal Curve Signing Handbook

Horizontal curves are a necessary component of the highway alignment; however, they tend to be associated with a disproportionate number of severe crashes. Warning signs are intended to improve curve safety by alerting the driver of a change in geometry that may not be apparent or expected. However, several research projects conducted in the last 20 years have consistently shown that drivers are not responding to curve warning signs nor complying with the Advisory Speed plaque. The procedures described in this handbook are intended to improve consistency in curve signing and driver compliance with the advisory speed. The handbook describes guidelines for determining when an advisory speed is needed, criteria for identifying the appropriate advisory speed, an engineering study method for determining the advisory speed, and guidelines for selecting other curve-related traffic control devices. The handbook is intended for use by traffic engineers and technicians that have been given the responsible charge of evaluating and maintaining horizontal curve signing and delineation devices. The procedures described in this handbook are applicable to rural highways. However, they may be useful for establishing advisory speeds for urban streets.