(a) The operator of a bus shall not stand or park such vehicle upon any street at any place other than at a bus stand so designated as provided herein.
(b) The operator of a bus shall not stop 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 as provided herein, 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 wheels of such vehicle not farther than twelve (12) 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 in the central traffic district at any place other than in a taxicab stand designated as provided in sections 18-139 and 18-140. This provision shall not prevent the operator of a taxicab from temporarily stopping in accordance with other stopping or parking regulations at any place for the purpose of and while actually engaged in the expeditious loading or unloading of passengers.