Nationwide Differential GPS System

Overview
The purpose of the Nationwide Differential GPS System (NDGPS) is to provide accurate positioning and location information to travelers, emergency response units, and other customers. The system provides 1- to 3-meter (m) navigation accuracy. This will improve collision notification systems, enable cooperative vehicle-highway collision-avoidance systems, and provide more accurate in-vehicle route guidance systems.

Source

 * U.S. Department of Transportation, Federal Highway Administration, Nationwide Differential Global Positioning System Program Fact Sheet (full-text).