Assessing Stopping and Passing Sight Distance on Highways Using Mobile LiDAR Data

Abstract

Geometric design guides provide minimum standards that must be met to ensure the safe and efficient operation of highways. One of the most important elements when designing a highway is the sight distance available to road users. Designing safe highways involves ensuring that this distance exceeds the minimum distance required by drivers negotiating different segments of a highway. If the sight distance available is less than that required, the likelihood of a driver safely completing a certain maneuver decreases. Measuring the available sight distance along a highway and ensuring that minimum design standards are met often requires field visits or graphic analysis of as-built drawings. Although these techniques are effective, they require significant time and effort. As a means of reducing the burden associated with sight distance assessment and in an attempt to help proactively address sight distance limitations on roads, this paper proposes an process by which sight distance along a highway can be automatically assessed on Light Detection and Ranging (LiDAR) point cloud data collected on test highways. The data was first used to create a digital surface model; “observer” and “target” points are then defined along the highway’s travel lanes. After that, the line of sight assessment is conducted to determine the existence of obstructions between the pairs of observer and target points. An algorithm to calculate the available sight distance based on the outputs of the Line of Sight assessment is then developed. The algorithm was tested on two different highway segments in Alberta, Canada, and was successful in determining the available sight distance in both cases. The extracted information was then compared to theoretical sight distance values, and it was found that the minimum stopping sight distance (SSD) was met in all but a small region of one of the segments. Moreover, a passing sight distance (PSD) assessment also revealed that minimum requirements were not met at one of the passing zones in one of the segments. Finally, collision records for locations where sight distance was limited were examined, and it was found that sight distance limitation could have been a factor in collision occurrence.