Trolly Etiquette

A and B are the operators of the trolly.  B walks at the front of the trolly with one hand holding the trolly gently while maneuvering it around corners.  A walks holding the handlebars using force to push the trolly and to stop it when appropriate (accelerate and decelerate).  Without A, B is just maneuvering the trolly, stationary.  B cannot really operate the trolly without A.  A can operate the trolly without B (it is just a bit more difficult).