Current developments in truck design may worsen the problem of runaway trucks. Trucks are becoming heavier, and the design of more aerodynamic cabs and the use of radial and smaller-diameter tires may increase the potential for brake failure on downgrades. This report gives State transportation officials an overview of the Grade Severity Rating System, a program to reduce runaway truck accidents through the use of weight-specific-speed (WSS) signs. The report contains adequate information for State transportation officials to decide whether they want to implement GSRS-WSS and also tells potential users where to get the additional information needed for actual implementation. The report summarizes the five steps required to implement WSS signing. The first step determines the magnitude of the runaway truck problem in a given State and identifies potential WSS sites. The second step analyzes the sites selected to determine percent and length of downgrade and truck braking length - the variables that determine brake temperature and hence safe speeds for different truck weight classes. In step three, analysts enter percent of grade and grade length or truck braking length into a computer program that yields advisory speeds for various truck weight classes. Step four converts the computer program output into the information that will actually be posted on WSS signs. Step five is actual installation of signs before and preferably along the downgrades selected for WSS. The report is based on the following studies: Feasibility of a Grade Severity Rating System, FHWA/RD-79/116, The Development and Evaluation of a Prototype Grade Severity Rating System, FHWA/RD-81/185, Field Test of the Grade Severity Rating System (GSRS), FHWA/RD-86/011, and Grade Severity Rating System (GSRS)--Users Manual, FHWA-IP-88-015. (Author/publisher)
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