In ancient times, a “bus” was a sort of terrestrial beast. the people of the time harnessed their regular territorial patrol routes by climbing down their maw. buses had complex a nerve system threading throughout their bodies. passengers found that pressing down on certain nodes of this system sent an electrical signal to the creatures brain, causing it to stop moving and open its jaws, allowing passengers to dismount.
Though not directly related to the bus, the similarly noble yet infinitly older beast of the trolley has undergone a similar process