Transportation Distance Measurement Data Quality

Data quality and spatial data accuracy issues are critical to any geographic information systems ~GIS! application, especially GIS applications in the transportation community. This paper addresses one specific aspect of spatial data accuracy issues, namely, linear measurement ~length measurement!, through a transportation case study. In the case study, an alternative to distance measurement instruments ~DMI! was proposed to determine road lengths for interstate highways in North Carolina. In the proposed alternative, the road lengths were calculated by overlaying GIS roadway linework over elevation data—in this case the National Elevation Dataset, which was developed based on U.S. Geological Survey 7.5 min digital elevation models and calculating a centerline roadway slope distance. The results of this approach were collected and compared with DMI lengths to assess the accuracy of the proposed approach. Error sources were tentatively identified and control mechanisms were discussed. Computer tools and models used to model surfaces and roadway linework are emphasized in this paper. The computer algorithms used for length calculations and accuracy assessment are described. This research concluded that, by carefully controlling quality of both the roadway linework data and the elevation data, GIS programs can be written to provide accurate length measurements to the transportation community. Furthermore, instrumentation like global positioning systems, high resolution cameras, and precise odometers can be combined to create productivity enhancing automated engineering systems.