Traffic Sign Sight Distance for Low-Volume Roads

Warning signs are a critical signaling element providing information to the monitoring public with respect to potential hazards on the roadway. They should be placed in order to allow the driver enough time to perceive, identify, and decide on and perform any necessary maneuvers. Although stopping-sight distance is adequate for most design situations, some situations require drivers to perform complex maneuvers or make immediate decisions, such as when drivers must respond to an unexpected maneuver, for example, at an intersection or dangerous curve. In these areas, the sight distance of a warning sign is of fundamental importance so as to allow drivers to respond appropriately and to perform the proper maneuver. The placement of the road sign is an integral part of road design; in fact, its correct definition, or rather the choice of the location of the different signs in relation to the geometrical and functional characteristics of the road, represents one of the fundamental tools for improvement of road safety. Such a concept is extremely important for existing roads and, in particular, for those with a low traffic transit. The effectiveness of the sign is subordinate to its perception–response time and therefore to the capacity to influence drivers’ speed in order to make it compatible with the road geometry. Therefore, a mathematical model was specifically developed to investigate the relationship between sight distance and sign location according to the "Manual on Uniform Traffic Control Devices." To carry out this analysis, a survey was performed on warning curves with inadequate sight distance by using traffic counters capable of recording the 85th percentile speed of vehicles.