I'm not sure how BL's are laid out in Southern Maine. In CA they are solid, until they approach intersections, when they become broken dashed, whatever.
I would say solid lines indicate to cars that they are to stay out of the bike lane unless they are entering/exiting a driveway. The broken lines at intersection indicate it is OK to for autos cross for a turn, and also alerts the cyclist that the sanctity of the bike lane may become violated by automobiles in this area.
For the record, I will ride in a bike lane if it happens to be the correct lane position for a given situation, but correct lane position is paramount, whether there are bike lanes or not.
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Fewer Cars, more handlebars!