Gee, imagine thinking roads should be used by more than cars. I don't know that there are any laws concerning it, but I have noticed where I live, Albuquerque, New Mexico USA, that bike lanes seem to be getting marked on many roads when resurfaced. This generally requires narrowing the traffic lanes which I believe is known to slow traffic. Of course, white lines aren't force fields, but they still work well to make it clear that vehicles need to stay between them.