(a) No person shall stop, stand or park a vehicle other than a bus in a bus stop, or other than a taxicab in a taxicab stand, when any such stop or stand has been officially designated and appropriately posted, except that the driver of a passenger vehicle may temporarily stop therein for the purpose of, and while actually engaged in, loading or unloading passengers when such stopping does not interfere with any bus or taxicab waiting to enter or about to enter such zone, and then only for a period not to exceed three minutes, if such stopping is not prohibited therein by posted signs.
(b) No operator of a bus shall stop, stand or park such vehicle upon any street or other public way at any place for the purpose of loading or unloading passengers or their baggage other than at a bus stop so designated and posted as such, except in case of an emergency.
(c) No operator of a bus shall fail to enter a bus stop on a street or other public way in such a manner that the bus when stopped to load or unload passengers or baggage is in a position with the right front wheel of such vehicle not further than eighteen inches from the curb and the bus approximately parallel to the curb so as not to unduly impede the movement of other vehicular traffic.
(d) No operator of a taxicab shall stand or park such vehicle upon any street or other public way at any place other than in a taxicab stand so designated and posted as such. This provision shall not prevent the operator of a taxicab from temporarily stopping in accordance with other stopping or parking provisions at any place for the purpose of, and while actually engaged in, the expeditious loading or unloading of passengers.