(a) No person shall step, 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) The operator of a bus shall not stop, stand or park such vehicle upon any street 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) The operator of a bus shall enter a bus stop on a public street in such a manner that the bus when stopped to load or unload passengers or baggage shall be in a position with the right front wheel of such vehicle not further than 18 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) The operator of a taxicab shall not stand or park such vehicle upon any street 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.