Abstract The current method of checking police-reported road accident data involves a rigorous process of manual and computer validation, with the objective of removing all the errors that exist on the accident report forms. This paper shows how a geographic information system (GIS) can be used to identify mistakes that exist in several locational variables once this process has been undertaken. It compares items contained on the accident report form with accurate highway feature information obtained from other sources. There were less than 10% of mistakes for the variables of district, speed limit, road class, and road number; less than 20% for junction control, junction detail, and pedestrian crossing facilities; and over 20% for carriageway type. If highway data were routinely entered onto a GIS by all British highway authorities, the above variables might not need to be entered by the police on their accident report forms.