To track lift trucks and other vehicles at a dozen of its distribution centers in the United States, Wal-Mart has been using an RFID-based system.
The vehicle management system (VMS) consists of a battery-powered 915 MHz RFID transceiver built into a vehicle asset communicator--a small computer that mounts onto a lift truck or other vehicle. The VAC uses a proprietary air-interface protocol to communicate data to receivers known as wireless asset managers, mounted throughout a DC. The number of these receivers installed at a particular DC varies depending on the facility's size. The wireless asset managers then pass the data they collect to software running on a central server within the facility, either via a wireless or wired (ethernet) link.
The software processes each tag's location and sensor data, and can tell DC managers everything from where a specific vehicle is located within the facility, to who is driving the vehicle, whether it is carrying a load and if it requires maintenance. It can also save and aggregate this data for each vehicle to provide lifecycle visibility.
Source: RFID Journal, http://www.rfidjournal.com