Estimating lives saved and serious injuries reduced by bicycle helmet use in Colorado, 2006-2014.

Using the methodology developed by the National Highway Traffic Safety Administration (NHTSA) for motorcyclists, this paper estimates bicycle helmet effectiveness factors (HEFs), defined as the percentage greater chance that a helmeted bicyclist will avoid a fatality or serious injury relative to a non-wearer. We analyse reported motor vehicle-bicycle collisions in Colorado between 2006 and 2014. We conclude that NHTSA's motorcycle HEF methodology did not provide reasonable results given underreporting of low-severity collisions of helmeted bicyclists. The HEF methodology may be applied to bicycles in future research if more complete bicyclist collision reporting can be obtained. To account for underreporting, we calibrated our bicycle HEFs to past research and found that approximately one of every two bicyclists killed may have survived (HEF = 0.50) and one of every three seriously injured bicyclists may have been less seriously injured (HEF = 0.33) if wearing a helmet at the time of the collision.