I actually think this is more important reversed... its more important for pedestrians to be cautious crossing... in good weather one can usually assume if one steps into a crosswalk, cars will stop and let you walk (its a $100 fine in Mass not to yield to a pedestrian in a crosswalk). However if the roads are bad enough that the crosswalk is not visible, its possible that even if a driver attempts to stop they may slide through the crosswalk and potentially hit you in the process accidently. Just because the law says you have to yield does not take into consideration that sometimes stopping is not possible given conditions.