The law states that when a bicyclist is in the roadway or riding on the yellow line along the shoulder, motorists will need to cross the center lane to pass a bicyclist safely. And if the traffic is not clear, or a blind hill is approaching, the motorist would be legally required to slow down behind the bicyclist until it’s safe to pass.
[From http://www.whio.com/news/new-law-starts-today-drivers-must-move-over-pass-bicyclists/LDAsIKqd7T96mn6bHvCjfL/ ]
B' Spokes: Maryland's law says basically pass safely unless... And if you don't understand the legal technical terms (like too many police) it might as well say pass safely unless you can't. But my main point in sharing this they specified that sometimes it is necessary to slow down and wait behind a cyclists till you can pass safely.