A system is disclosed for tracking and controlling shopping carts and other types of human propelled vehicles. The system includes a wheel assembly that attaches to a cart. The wheel assembly includes a brake unit for inhibiting cart motion, and includes wireless communication circuitry. The wheel assembly is capable of activating the brake unit in response to one or more conditions, such as the receipt of an RF signal or command. In some embodiments, the system also includes a display unit that displays information to a user of the cart, including information regarding the cart's proximity to a lock zone in which the brake unit will become activated.