The League of American Bicyclists (LAB) is reporting that S. 1813, the Senate draft transportation authorization bill, contains a mandatory sidepath law that would require cyclists to ride on sidepaths on federal land. The LAB article has much more information on why such is a terrible idea. But if you have non-cycling friends who are wondering why such proposals actually do
not promote safety, here are a few reasons.
First, the vast majority of car-bike crashes take place at intersections. Riding on a sidepath is dangerous for the same reasons sidewalk riding tends to be dangerous. Behavior at intersections is complicated by the presence of a sidepath. Car drivers do not typically look for same direction cyclists passing from the right, when making a right turn (right-hook conflict). Cyclists are also less visible to oncoming traffic, which may be planning to make a left (left-hook conflict).
Second, many sidepaths are maintained well below the standards of main roads. Debris tends to accumulate, and cracks and potholes tend to accumulate to a larger degree before remedial action is undertaken.
Finally, travel at higher speeds (say anything above 10 mph) is difficult to do safely when riding on even a well-maintained sidepath since there tends to be insufficient room to maneuver.
None of these facts are obvious to a non-cyclist. The proposal seeks to get cyclists "out of the way" of car traffic, even traffic traveling at a modest 30 mph. In practice, passing cyclists is something that drivers routinely accomplish within a minute or two at most.