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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.

IntroductionIn the spring of 1995, the Metropolitan Atlanta Rapid Transit Authority (MARTA) contracted with a team of consultants and researchers to implement an Intelligent Transportation System (ITS). The purpose of this system was to create a showcase of technology for the 1996 Summer Olympic Games and to leave MARTA with a legacy that would improve transit performance and increase ridership in the long term. The project put in place at MARTA three areas of technology: 1) Advanced Traveller Information Systems (ATIS) that provide an automated means of assisting MARTA patrons with travel information, 2) Automatic Vehicle Location (AVL) for tracking bus positions in real time, and 3) an interface with Georgia Department of Transportation's Advanced Transportation Management System (AIMS) so that up-to-date traffic and road condition information could be made available to MARTA.At the core of the MARTA ITS is a series of spatial and attribute databases that provides critical information to all of the different ITS applications. One of the transit features that is described in these databases is the bus stop. Bus stop data are of particular importance to the MARTA ITS because they are used by so many different applications. The attribute data associated with each bus stop is as extensive as any other bus stop inventory that currently exists in the United States. The database contains more than 60 fields that provide detailed location information and the physical characteristics of the bus stop and the surrounding area.

CHAPTER 8. DEVELOPING THE GIS 47 8.1 Data Formats 47 8.2 The GRASS GIS Software 48 8.3 Developing the GIS with GRASS 49 CHAPTER 9. ANALYSIS OF RESULTS 9.1 Coordinates Comparison 9.2 Statistical Analysis 9.3 Economic Analysis of the Survey Methods Used CHAPTER 10 CONCLUSION AND RECOMMENDATIONS 10.1 Conclusion 10.2 Recommendations BIBLIOGRAPHY