Quality of WIM Data

The quality (accuracy, reliability and stability) of the measurement data used in any application the quality of the results and effects. Hence the quality of the WIM data must be verified using Data Quality Checks. In general, the checks will look at the stability of certain elements or characteristics of the measured data. The following examples of such characteristics can be used in the quality checks:

  1. The vehicle length of truck + trailer combinations and that of tractor + semi-trailer (articulated) combinations. E.g. for most EU member states the maximum allowable lengths for these combinations are respectively 18.75 m and 16.50 m;
  2. The gross vehicle weight (GVW) of 3 axle trucks and that of 5 axle tractor + semi-trailer (articulated) combinations. E.g. for international transports in most EU member states the maximum allowable GVW’s for these combinations are 26 tonnes and 40/44 tonne respectively;
  3. The axle load of the first (steering) axle of the fully loaded 5 or 6 axle articulated vehicles. International experience has shown that for the fully loaded vehicles the load on this axle lies normally in a relatively narrow bandwidth;
  4. The axle distance between the 2nd and 3rd (driven) axles of 6 axle tractor + semi-trailer combinations. International experience has shown that the distance between these axles is very stable at 1.30 to 1.35 m, as this allows the highest axle loads.

Besides the weight and length related tests, other parameters should be checked to provide an indication of the correct operation of the WIM system:

  • The variation in the number of registrations per day;
  • The number or percentage of unclassified vehicles – or classified as ‘Other´ – per day;
  • The number or percentage of measurement or system errors per day;
  • The number of hours without registration (between 04:00 and 24:00h)