By today's standards, most producers are happy to know their trucks are driving through the right subdivision, hoping the driver can find the customer's pickup. In the near future, governmental policy changes governing the control of the satellite-based Global Positioning System (GPS) will enable producers to pinpoint their deliveries and employee activities.

Department of Defense (DOD) engineers developed the GPS to monitor troop movements and deploy weapons. The system's master control center currently provides two levels of service: a precise positioning service for defense purposes and an encoded standard positioning service for civilian use. System engineers create the difference in GPS service levels by adding a position error known as "selective availability." This dual system may soon become one.

The federal government has recognized the need to increase the availability of GPS technology. In 1996, responding to the question of how GPS fits in national defense plans, the Office of Science and Technology Policy's National Security Council issued a fact sheet that recommended eliminating the dual-service system by 2006. Beginning next year, the president will receive an annual report from GPS system managers on the military need to continue adding the selective availability.

Last January, Vice President Al Gore announced a $400 million GPS modernization program that would add two new civil signals. Each new civil signal would require the addition of 18 Block HF satellites to ensure users of worldwide 24-hour signal capabilities. Even with the best estimates of federal funding, the first of the new stand-alone civilian GPS systems wouldn't be fully operative until the end of 2009.

To reduce this waiting period, in October 1998 near a Nebraska cornfield, technicians with the USDOT began working with other government agencies to develop nationwide availability of highly accurate GPS signaling. The Nebraska location is the first of a series of radio stations that will become a nationwide civilian geolocation system in 3 to 4 years. This National Differential Global Positioning System, or NDGPS, will correct not only the selective availability errors intentionally placed on GPS by DOD engineers but also those errors inherent in any satellite-based location system, such as atmospheric effects and satellite operating parameters. This new civilian-oriented system provides accuracy to within 3 meters nationwide.

Some engineering challenges will emerge before the system is fully in place. There are concerns that new closer stations may create areas of increased frequency interference. Another concern is the balance between the necessary signal strength with station location; fewer stations require a stronger signal, potentially creating more signal interference. Then there's the problem of land-based obstacles that can block radio transmissions.

When the USDOT's system is in place, planners hope to enhance the country's total transportation effort. Using GPS signals, the software can locate a truck to within the nearest street. With NDGPS, the software lets the dispatcher know, by number, if the truck is on the correct lot.

In many areas where NDGPS's higher accuracy is available, most producers elect not to use it. But in the near future, producers may want to consider the higher accuracy.

This article includes an article by Daniel Sovocool on potential legal issues with GPS. There is also a table of interesting applications underway to improve transportation.

Keywords: National Differential Global Positioning System, selective availability, GPS, dispatch, track, satellite, Intelligent Transportation System, ITS, automatic vehicle location, AVL, legal