In order to properly compare the two traffic counting systems, both the radar vehicle detection equipment and the inductive loops should be evaluated for their reliability and cost effectiveness.
Findings: Currently, inductive loops are used to count traffic at the 52 permanent sites located in South Dakota. Because they are located within the pavement, the loops are susceptible to being destroyed during maintenance projects. When they are destroyed, it is necessary to close traffic in that lane, cut a loop into the pavement, and fill the void left in the concrete. This study explored the potential implementation of a non-intrusive sensor, the RTMS. The RTMS is installed adjacent to the roadway so it is not at risk of being destroyed when maintenance is performed.
In this study, the RTMS was evaluated for both its cost effectiveness and reliability. From manual counts, it was found that the RTMS tended to count 3 percent low. It was more accurate than road tubes, which were also used to compare to the manual counts. According to the Office of Data Inventory, the accuracy of the inductive loops is dependent on the counters that they are run through.
The initial cost of the RTMS tends to be higher than that of inductive loops. But, if the pavement is in poor condition, it is probable that the loops will be in need of replacement before the end of their expected lifetime. This will cause the lifetime cost of the inductive loops to be more than that of the RTMS. In the case of speed surveys, the inductive loops are far less expensive to implement than the RTMS.
Due to its reliability, it was determined that the RTMS should be implemented if it is cost effective. In other words, if the lifetime cost of implementing the RTMS is less than or comparable to that of the inductive loops, it should be implemented. Otherwise, the inductive loops should be reinstalled at that location. Other potential implementations of the RTMS, such as a mobile counting station, were explored as well.
Due to problems the Minnesota DOT found with the predecessor to the RTMS used in this study, it is recommended that further testing be done on the RTMS to verify that it counts traffic accurately during snow, rain, and freezing rain.