Actual incidences of road casualties, and their injury severity, modelled from police and hospital data, France

Background: Nation-wide road casualty figures usually come from police data. In France, as in many developed countries, the reporting of fatalities is almost complete but the reporting of non-fatal casualties is rather low. It is moreover strongly biased. Valid estimates are needed. Methods: Using the capture-recapture method on police data and on a road trauma registry covering a large county of 1.6 million inhabitants, we estimate police under-reporting correction factors that account for unregistered casualties. These correction factors are then applied to the nation-wide police data, with standardization on under-reporting bias factors. Results: In 2004, whereas the police report 108 727 non-fatally injured, the estimation yields 400 200. Over the 1996-2004 study period, the average annual estimated incidence is 871/100 000 for all injured (3.4 times the police incidence), 232/100 000 for hospitalized, 103/100 000 for seriously injured (2.2 times the police incidence) and 12.6/100 000 for casualties with long-term major impairment. The incidence of seriously injured (NISS 9+) is 11.3/100 000 for pedestrians, 9.5/100 000 for cyclists, 36.3/100 000 for motorized two-wheel users and 42.5/100 000 for car users. Conclusions: The estimated incidences are much higher than the police-based ones. This changes the scale of the road injuries issue. The risk of suffering a major impairment from a road crash is equal to the risk of being killed. Motorized two-wheel users experience a large burden of traffic casualties, much larger than that indicated by police data. The approach used can be reproduced in other countries, if an additional medical registration exists.