Surveys of goods vehicle weights were carried out by TRL between September 1990 and January 1991 at four sites at which weigh-in-motion (WIM) equipment is used to select goods vehicles for enforcement weighing. At each site vehicles were weighed using both a two-sensor piezo-electric WIM system, which measures the dynamic weights of the axles of vehicles travelling at normal highway speeds, and on an enforcement weighbridge, which measures static axle weights. The survey data was used to evaluate the use of WIM systems for the selection of goods vehicles for enforcement weighing. The pre-selection systems were found to be inefficient. The average `hit' rate (percentage of selected vehicles found to be overloaded) was 23 per cent and the average `miss' rate (percentage of overloaded vehicles on the road not selected) was 70 per cent. The efficiency of pre-selection could have been improved by using multiple sensor arrays or providing the WIM systems with `plated' weight limits using transponders fitted to the vehicle. The WIM systems were also found to be unsuitable for monitoring road wear factors. (A)
Abstract