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GPS APPLICATIONS AND REQUIREMENTS 42 For future ITS applications of GPS, such as automatic vehicle control and collision avoidance, integrated systems that use inertial navigation units and differential corrections will be required to meet the stringent accuracy, integrity, and availability requirements placed on any system that is fundamental to public safety. Current legal limitations, which restrict the ability for private sector interests to provide ''navigation" services as opposed to "positioning" services, however, may negate the ability to use private sector DGPS providers to help meet these requirements. Although the removal of SA would not allow the standard positioning service to meet these requirements either, it would improve the performance of both wide-area differential systems such as the WAAS, and local-area systems.33 The Cost of Integrated Systems Land transportation seems to offer unlimited opportunities for integrating GPS and DGPS with other complementary technologies related to communications, scanning, and digital imaging. Example technical systems include cellular phones, on-board fax and computer resources, driver performance and alertness equipment, and vehicle operations sensors. It seems reasonable to suggest that private sector creativity will be able to devise these integrated systems that will likely form the core of the nation's future transportation systems such as ITS. A few words of caution, however, should be considered. In order for these systems to be widely accepted by potential users, their cost must be considered modest; they must be easy to use; and the equipment itself must be durable, reliable, and essentially maintenance free. "Gadgets" that fail to meet the above criteria or compromise the operational safety of a vehicle will never be accepted voluntarily by users in the surface-transportation community, especially the competitive commercial vehicle market. In addition, integrated positioning and communications systems utilizing GPS and other technologies will be most widely accepted if they help to fulfill bonafide publicand private-sector customer needs in a cost-effective manner. Systems introduced to the marketplace because of technology push are not likely to achieve widespread success. Findings There is a tremendous market for land navigation and positioning systems that integrate GPS with other technologies such as digital communications systems, driver performance and alertness equipment, vehicle operations sensors, and CD-ROM-based digital mapping and applications software. These systems, however, will only become widely accepted if costs continue to drop, high levels of reliability can be maintained, and reasonable durability can be assured. 33 Potential improvements to DGPS techniques as a result of the elimination of SA are discussed in the next chapter.
