Quantifying Road Grade Based on In-Vehicle Measurements with Global Positioning System Receivers

摘要

Variability in real-world vehicle fuel use and emissions during a trip depends primarily onvehicle speed, acceleration, and road grade. However, there is not a standard method formeasuring road grade from a moving vehicle. Changes in road grade of more than a percentagepoint significantly affect fuel use and emission rates. Consumer grade Global PositioningSystem receivers with barometric altimeter (GPS/BA) are used to measure position andelevation. Data were collected from 12 vehicles, each using 3 GPS receivers, for a total of 36repeated GPS/BA runs on eight one-way routes in the Research Triangle Park, NC region. Roadgrade was estimated by combining data from 9, 18, and 36 runs and applying linear regression tonon-overlapping and adjacent road segments of length Δd. The accuracy of the estimated roadgrade was evaluated based on comparison to estimates from aircraft-based LIDARmeasurements. The average grade is found to be accurate. The average precision is 0.39, 0.25,and 0.16 percentage points, for sample sizes of 9, 18, and 36 runs, respectively, among 1,116individual road segments. The proportion of segments that have road grade precision within atarget of ±0.5 percentage points are 80 percent for 9 runs, 98 percent for 18 runs, and 99.8percent for 36 runs. Thus, the use of a low cost GPS/BA is a promising approach for accurateand precise measurement of grade relative to data quality needs for quantifying variability in fueluse and emissions.