Zone-based control of cart usage using RF transmission for brake activation

A system for controlling usage of carts, comprising:

• a plurality of wheel assemblies that attach to respective human propelled carts, each of the wheel assemblies comprising a wheel, a brake unit for inhibiting cart movement, and communication/control circuitry;
• a first antenna that repetitively emits a transmission of a first command that instructs the wheel assemblies to activate their brake units, said first antenna positioned to create a first zone in which cart movement is inhibited;
• and
• a second antenna that repetitively emits a transmission of a second command that instructs the wheel assemblies to deactivate their brake units, said second antenna positioned to create a second zone in which cart movement is not inhibited, said second zone located adjacent to the first zone such that a cart with an activated brake unit can be moved from the first zone to the second zone to cause its brake unit to become deactivated;
• wherein at least one of said antennas is a directional antenna that is mounted above ground and positioned to radiate downward toward a ground surface on which the carts move.