Imagine driving a three-story house while using only a few small windows, and you will have an idea of what it is like driving many of the dump trucks currently used in surface mining. A system combining GPS receivers, rugged computers, and wireless communications tells equipment operators the location of nearby equipment and obstacles, and warns them when they get too close. Think of the biggest vehicle you have ever driven - perhaps a large rented moving van. Make that vehicle 25 times bigger and increase its load capacity by a factor or 100 - but cut driver visibility to a small fraction. Now picture yourself maneuvering this behemoth inside an open pit mine, around fixed obstacles, other moving vehicles, and workers on foot. That is the daily challenge for the operators of the giant dump trucks used in surface mines. As a result, each year, an average of 20 accidents and three fatalities occur involving collisions between a piece of surface mining haulage equipment and either a smaller vehicle, a worker, or some other object. Another 21 accidents occur and three mining equipment operators are killed each year when their equipment backs over the edge of an embankment, stockpile, or dump point. Gray areas indicate where the driver cannot see. To help prevent these accidents, researchers at the Spokane Research Laboratory of the National Institute for Occupational Safety and Health (NIOSH), in cooperation with a large GPS manufacturer, are developing a proximity warning and edge detection system based on differential GPS technology and wireless network communications. This system provides equipment operators with the locations of nearby equipment, small vehicles, workers on foot, and stationary obstacles. To be effective, this system requires an accuracy of two meters or better. We tested the first prototypes in a parking lot on passenger cars. Since then, we have developed a mine-ready system, consisting of a GPS receiver and antenna, a small computer with LCD display, proximity warning software, and a 900-MHz Internet protocol (IP) radio. We tested the system at the Phelps Dodge Mine in Morenci, Arizona, on two pieces of haulage equipment and two service vehicles.