Speed correction for SCRIM survey machines

The levels of skid resistance on the Highways Agency’s (HA) network are routinely monitored using SCRIMs. The survey results from these machines are speed dependent and the data collected is corrected to a standard test speed of 50km/h before use. On the Highways Agency network the target test speed for the routine surveys is 80km/h on roads with a speed limit greater that 50mph (if the SCRIM is fitted with dynamic vertical load measurement) and 50km/h on all other roads. The current speed correction formula (detailed in HD28/04) has been found to overcorrect data collected at the higher speed (80km/h), particularly for middle to low levels of skid resistance. This report covers the work conducted to develop a new speed correction formula for SCRIM. This involved tests at a range of speeds on TRL’s test track, the Twin Straights facility at MIRA and stretches of the M27 and M3 motorways. The sites were selected so that they covered the range and combinations of SR and texture found generally on the network.