Road Cross Slope Evaluation Using Surveying and LiDAR Techniques

The cross slope is a critical geometric feature of pavement surfaces as it affects safety due to its relationship to the potential of hydroplaning during wet weather. Appropriate cross slopes provide adequate drainage, so water will run off the surface to a drainage system such as street gutters (urban streets) or side ditches (rural facilities). An inadequate cross slope could lead to several safety issues, including hydroplaning, loss of control, and run-off-road crashes. This research study compared two methods of data collection, namely a conventional survey and a LiDAR-based survey using a terrestrial laser scanner, to evaluate roadway surface’s cross slopes. Two existing rural road segments in San Luis Obispo County (California, USA) were selected for evaluation. A comparison between the results from the two methods showed that the difference follows a normal distribution, indicating no systematic errors during data collection. Also, the two-sided paired t-test between the traditional survey surveying and LiDAR shows no statistically significant differences between the slopes estimated using the two methods. Moreover, the results indicate that the difference between LiDAR-derived cross slopes and field surveying measurements is less than 0.2% at a 95% confidence level.