A bicyclist is riding on two very narrow, high-pressure tires. Fairly small rocks can deflect a bicycle wheel, a minor ridge in the pavement can cause a spill, a pot-hole can cause a wheel rim to bend.
Wet leaves are slippery and can cause a bicyclist to fall.
The gravel that gets blown off the travel lane by traffic accumulates against the curb, in the area where bicyclists are riding. Thus, it is important to properly maintain existing facilities. Bikeways will always be subject to debris accumulation and surface deterioration. Adequate maintenance will help to protect the investment of public funds in bikeways, so they can continue to be used safely. Poorly maintained facilities will become unusable and they may become a legal liability.