Hey Seattle Forest -- thanks for posting this.
BTW, the second "elsewhere" link you provided links to "Personal and trip characteristics associated with safety equipment use by injured adult bicyclists: a cross-sectional study" and I couldn't find the route-specific information. It seemed to be more focused on helmet and light usage.
Putting aside the question of severity, do you know what the authors mean by "risk"? Is it the probability that a cyclist using a particular route will have an accident? Or that an accident on a particular route is more likely to result in an emergency room injury?
I don't understand why they are comparing to "control" sites or concerned about "observer bias" if they are measuring rates (which is why I'm asking about how they define risk). Seems like this would be an empirical discussion and that they would be measuring traffic volume on the various routes.