Having caught up with a streetcar that has stopped to load or unload passengers, the driver of a vehicle must stop behind the streetcar until it finishes loading and unloading passengers and until all persons who have alighted from the streetcar have finished crossing or are no longer trying to cross ahead of the vehicle on the left side of the streetcar; provided, however, that, if there is a safety zone in place to ensure the safety of persons boarding and alighting from a streetcar or if no person is boarding or alighting from a streetcar and it is possible to maintain a distance of at least 1.5 meters from the left side of the streetcar, a vehicle may pass the streetcar on its left side at a reduced speed.