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Global Positioning System with an Attitude: Method for Collecting Roadway Grade and Superelevation Data

The use of a specialized Global Positioning System (GPS) to conduct high-speed surveys of roadway alignment, grade, and cross-slope characteristics is discussed. The system uses a single GPS receiver that has 24 channels monitoring four separate antennas (six channels each). The collection of attitude (heading, pitch, and roll) is made possible through the relative orientation of the antennas. By mounting the system on a road surveillance vehicle, accurate grades, superelevation, and crown measurements can be made without differentially correcting the GPS data. However, to gather precise positional data that correspond to the roadway measurements, differential correction with a GPS base station at a fixed known point is required. The design and use of this attitude GPS unit are addressed. Accuracy specifications for static testing are provided along with techniques to maximize this accuracy. Kinematic data collection is depicted for a local road and a freeway off-ramp. The use of digital terrain modeling technology provides a promising graphic database representation of the roadway characteristics.