Maryland statute requires that if a shoulder (wide enough to park a car or drive an ambulance) or a bike lane is present, then cyclists must use that shoulder or bike lane instead of the roadway, except for when passing, making a left turn, crossing a right turn lane or merge lane, or when it is reasonably necessary to leave the bike lane to avoid debris or another hazardous condition.
There are two legal consequences of the statute. First, the police can give you a ticket if you ride in the roadway and none of the exceptions apply. Second, if a negligent driver collides with you while you are in the roadway, then the courts will deny you (or your estate) damages unless you can prove that one of the exceptions apply, under the doctrine of contributory negligence.
There are a number of symbolic consequences. More than 40 states allow cyclists in the roadway, leaving it to the discretion of the cyclist whether to ride in the shoulder or bike lane. Some people believe that this statute makes Maryland look less friendly to bikes than other states, or that cyclists have fewer rights than drivers.
MDOT and others argue that this law helps them to justify construction of bike lanes and shoulders to the automobile-driving public. Some also argue that the law simply codifies what good cyclists do anyway.
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