Tire-Pavement Traction, Demand and Availability 840071
The demand for tire-pavement traction in accidents often exceeds that which can be provided by the best of tires and pavements. It is, however, reasonable and technically feasible to provide for sufficient traction to accommodate the normal demands of traffic even under wet conditions. This raises the question of what is “normal traction demand”. The question is not easily answered because demand is determined by a mix of vehicles, and a variety of drivers and their varied reaction to a multitude of road conditions and traffic situations. The paper discusses the problem primarily from the pavement side. One way of attacking it is to relate wet weather or loss of control accidents to the available traction either globally or at location types at which accidents are likely to occur. This approach is not overly successful for a number of reasons which are discussed. An alternate approach is to observe actual traffic at selected locations, measuring the path and speed of every passing vehicle and computing their traction demand. The method is costly, but hard data are obtained, but to arrive at minimum values for the traction characteristics that tires and pavements should meet one must still make the decision of what level of traction demand is normal or reasonable. This and related questions are discussed in detail and illustrated by examples from a variety of sources. The authors conclude that minimum traction values that are to be mandated cannot be derived from research data and engineering considerations only, but must in the final analysis be set by the authorities having responsibility for traffic safety.