Static warning signs of occasional hazards: do they work?

Abstract

Highway agencies expend significant resources on the installation, upgrading and maintenance of traffic control devices. To ascertain that those resources are well invested, it is important to know whether traffic control devices serve their intended purpose. The answer may be easy for some traffic control devices such as traffic signals, regulatory signs and guide signs, but it may be more difficult for other devices such as warning signs in general and those intended for occasional hazards in particular. Examples of these occasional hazards are railroad crossings, icy bridges, unexpected alignment and/or geometry, falling rocks, wildlife crossings, etc. For regulatory and guide signs, drivers feel an “obligation” to use the information provided by those signs; in the case of warning signs, the use of information and drivers’ reactions seem to be based more on perception of risk. The effectiveness of static warning signs for occasional hazards is questionable because those signs typically are posted with out the hazard being perceived by drivers. Subsequently, highway agencies have begun to question the feasibility of expending significant resources on the installation and maintenance of these signs when little evidence exists regarding their effectiveness in improving highway safety. Knowing the effectiveness of these signs in improving safety is important for highway agencies to assess the feasibility of using conventional signs and whether alternative warning devices are required for a safer highway environment.