Use of Image Analysis to Estimate Average Stopped Delays per Vehicle at Signalized Intersections

Abstract

Average stopped delay has been used to determine the level of service (LOS) of signalized intersections. This work has mostly been done offline by using manual field observation methods, analytical models, and simulation software. Dynamic evaluation of the LOS of signalized intersections has been difficult because the use of conventional methods requires a large amount of labor and cost if such analyses were conducted periodically. However, many traffic operations centers wish to be able to coordinate surface street and freeway management when congestion occurs. It is demonstrated that image analysis can be used to dynamically determine average stopped delay. Two methods—the gap method and the motion method—were developed and compared with ITE’s field delay observation method. Traffic Software Integrated System software was used to create images of queued vehicles. To eliminate parallax problems, two simple assumptions were made: the queued vehicles were viewed from the direction normal to the pavement, and all lines of sight were parallel to the camera’s view direction. At present, the algorithms are simple, but they produced promising results. Various analysis time intervals from 1 to 20 s were used to estimate stopped delay. The gap method gave a good result when the time interval was about 15 s; the motion method produced a good result when the time interval was 1 or 2 s. The manual observation method resulted in a good estimate similar to that which the simulation software produced, especially when the time interval was about 10 s or less.