Applications of Supplemental Warning Devices

T“e capability of roadways to safely and efficiently serve vehicular traffic depends to a large extent on the adequacy of traffic control devices. The majority of motorists drive in an orderly and safe manner, provided they are given reliable regulatory and warning information. Motorists, through training and experience, develop expectations of when and in what manner they will be provided information necessary for safely controlling their vehicles. Motorists expect that similar traffic control devices always will have the same meaning and will require the same action, regardless of where they encounter them. This expectation has been enhanced by the use of uniform traffic control devices that enable motorists consistently to interpret the general intent of a device by its shape and color. While the advantages of uniformity far outweigh the disadvantages, there are some undesirable effects when complete uniformity is maintained. One of the principal disadvantages is that strict uniformity might result in the failure to adopt an improved device or procedure simply because it is not in common use. In addition, total uniformity would require the specification of a separate traffic control device for every conceivable roadway geometric and traffic operational condition. This would be a monumental task that undoubtedly would still not cover every situation, while simultaneously increasing the size of the Manual on Uniform Truffic Control Devices (MUTCD) with devices of limited application.’ All states have adopted the standards of the MUTCD as the basis for designing and installing traffic control devices. The states recognized the MUTCD as providing minimal requirements, and have incorporated additional devices and practices into their manuals, which address their specific roadway design and driver expectancy needs. Additional devices not included in either the federal MUTCD or the state manuals are developed frequently to provide motorist warning of roadway hazards that, ideally, should be eliminated. When the hazard is posed by unusual or unique conditions, the highway engineer is placed in the difficult position of identifying, or often designing, a warning device that provides a clear message to the motorist of the potential hazard. The Transportation Research Board (TRB), through the National Cooperative Highway Research Program (NCHRP), sponsored a synthesis of these supplemental warning devices. The purpose of the synthesis is to provide guidance to practicing engineers in developing warning signs for unusual geometric, operational and traffic control conditions not adequately addressed by standard warning signs. Information was obtained through a literature review and a state-of-the-practice survey. The survey was forwarded