Assessing Driving with the Global Positioning System: Effect of Differential Correction

Abstract

The Global Positioning System (GPS) offers new opportunities for the assessment of driving. GPS receivers acquire signals from a constellation of satellites to determine position. By logging position and time data, other kinematic parameters, such as velocity and acceleration, can be derived. Until recently, errors were intentionally introduced to reduce positional accuracy. Without the intentional degradation, it may be possible to use uncorrected data for assessment of driving. Differential correction can be performed by using a reference station to correct errors. GPS was used to determine the position, velocity, and acceleration of a vehicle. The main objectives were to compare corrected and uncorrected positions, velocities, and accelerations. Bland–Altman plots showed about two times as much error in the north–south position or velocity than in the east–west position or velocity when uncorrected data were compared with corrected data. Acceleration data showed no systematic differences between corrected and uncorrected data. Most errors between data sets could be explained by satellite geometry, transitions in the satellites being used, and the direction of travel. The greatest effect of differential correction was on position. Most uncorrected velocity and acceleration data would be acceptable for the assessment of driving. However, if positional information is needed, then correction should be done.