The number of seriously injured road users is used both as an indicator of traffic safety trends in Sweden and in more specific studies of, for example, different road user groups.

A seriously injured person is defined as a person who suffers injuries that lead to permanent medical impairment of at least 1 percent. The term very seriously injured is used as a complement and is defined correspondingly but refers to injuries that lead to permanent medical impairment of at least 10 percent.

In practice, the level of impairment is not known at the time of the accident, and therefore the number of seriously and very seriously injured persons are forecasted. The basis for the forecasts are Strada, the national database for road traffic accidents in Sweden, and a method developed by Folksam (a Swedish insurance company) that estimates the risk that a person’s injuries will lead to permanent medical impairment in the future.