Results: The likelihood that a given person walking or bicycling will be struck by a motorist
varies inversely with the amount of walking or bicycling. This pattern is consistent across communities
of varying size, from specific intersections to cities and countries, and across time periods.

Discussion: This result is unexpected. Since it is unlikely that the people walking and bicycling become
more cautious if their numbers are larger, it indicates that the behavior of motorists controls the likelihood
of collisions with people walking and bicycling. It appears that motorists adjust their behavior in the
presence of people walking and bicycling. There is an urgent need for further exploration of the human
factors controlling motorist behavior in the presence of people walking and bicycling.

Conclusion: A motorist is less likely to collide with a person walking and bicycling if more people walk or
bicycle. Policies that increase the numbers of people walking and bicycling appear to be an effective route
to improving the safety of people walking and bicycling.