Generally the higher the exposure rate (there are several ways to
consider this) the higher the body count. Fatalities obviously generally
occur from high speed differential impacts, but it doesn't take much
differential to make a fatal impact. A 20 mph impact is often fatal with
pedestrians, and while bicyclist impacts have different mechanics, the
the 20 mph figure is probably fairly accurate for bicyclists as well. I
was ringside, while on my bike, at a roughly 25 mph collision between 2
cars, and the energy involved was enormous.

I'm sure some of the fatalities involved getting hit from the rear, and
most of those will involve unlit bicyclists, but I'm also sure the bulk
are from turning/merging movements, and many of those will involve unlit
bicyclists too. Alcohol/impairment will often be involved for one or
both participants, and the percentage of children is another important
consideration.

Wayne