Include Bike Accident Data
Bicycle accident data could be used to come up with a bicycle safety rating for an area.
What Lyle and Richard said. Without normalizing for total number of cyclists per location, bike accident location data are a poor index of cyclist safety.
It would need to be accident rate, not just number, of course. It's not rocket science, but it's probably more work than the WalkScore people want to do.
One problem for this is that areas with more bicyclists are likely to have more total accidents, all else equal, but may still be safer because they have fewer accidents per bike trip.