More walking/biking leads to lower injury rate

Several studies in the past have indicated that as the amount of people walking/bicycling increases, the injury rate decreases. A recent study in Injury Prevention reinforces this conclusion and gives some reasons for it:

The common wisdom holds that the number of collisions varies directly with the amount of walking and bicycling. However, three published analyses of collision rates at specific intersections found a non-linear relationship, such that collisions rates declined with increases in the numbers of people walking or bicycling. . . .

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.