According to the Centers for Disease Control, the leading culprit in causes of death for people age 1-44 is unintentional injuries.  Motor vehicle collisions are included in this causal area, which is ahead of homicides, cancers and suicides.
Further, just because you turn age 45 doesn’t mean you’re risk goes down a lot- unintentional injuries remain the third largest cause for people age 45-64.
More information at: http://www.cdc.gov/injury/images/lc-charts/leading_causes_of_death_age_group_2014_1050w760h.gif