In 2011, the best performing countries recorded risk below five deaths per billion vehicle-kilometres. In the absence of data on vehicle kilometres for many IRTAD countries, the fatality rate per registered vehicles may be used as an approximation of exposure in order to describe risks and make comparisons between countries. Data on fatalities are usually reasonably complete, although police records miss a certain number of deaths resulting from crashes in all countries, and in all IRTAD member countries based on the same definition (death within 30 days of the crash), and therefore adapted for international comparisons.