Effect on Speed Distribution due to Intrusive and Non-Intrusive Portable Speed Measurement Devices

Abstract

Accurate traffic data are essential for supporting a multitude of transportation related decisions which affect transportation system operations, management, and planning. Advanced technology offers us various alternatives for accurately collecting traffic data. But accuracy of data is not just about the mechanical accuracy of the device, but it also about how people react when they see these devices installed either on roads or off roads. It is very important that the drivers should not get affected by the presence of these devices as these devices are not always to control the speeds but they are also installed to measure the true speed of the drivers. Such studies are the basis for important decisions, such as setting speed limits, timing traffic signals, placing traffic signs, and determining the effectiveness of the countermeasures. To evaluate the effectiveness on speed distribution due to the presence of various intrusive and non-intrusive portable speed measurement devices, automated traffic counters with pneumatic tubes, Smartsensor, Autoscope with camera trailer and Lidar gun were compared. Results showed that drivers did not react to pneumatic tubes and continued driving at the same speed; there was no significant difference in speeds at different locations while pneumatic tubes were installed. Drivers tend to react most by reducing their speeds when a Lidar gun was used, the Autoscope with camera trailer also effected driver behavior to a considerable amount. There was slight increase in speeds when the Smartsensor was installed. Similar driver behavior was observed when effect on the speeds of faster drivers was evaluated. For this analysis drivers driving above 85th percentile speeds were picked and tracked throughout the test site. Drivers reacted most to Lidar guns and then to the Autoscope with camera trailer. There was no significant difference in speeds when pneumatic tubes were installed.