In a recent answer I asserted
Statistics show that the probability of a collision rises rapidly after the speed difference between two road users exceeds 20 kph (12 mph). So choose paths without vehicle traffic, or roads with lower speed traffic.
User ebrohman requested a source for this. Since I remembered this "fact" from years back (er ... not only was it last millenium, it was from before the internet) I had to scrabble about to try to find an online source.
I found weak support for my thesis
... this US pdf Synthesis of Safety Research Related to Speed and Speed Management; it doesn't explicitly support the 20 kph claim. This Dutch pdf The relation between speed and crashes says at a collision speed of 20 km/h nearly all pedestrians survive a crash with a passenger car; again not the same as my claim ...
Intuitively, my claim makes sense. The greater the speed difference between a vehicle and me, the more likely a random driver is to make an error and collide with me.
But can we factually quantify how the risk varies with the speed difference?