Incident Detection with Traffic sensors on urban highways

by ryan fries, ph.d., p.e., mashrur a. chowdhury, ph.d., p.e., yongchang ma, ph.d., and anne e. dunning, ph.d. inTroducTion Traffic congestion is an increasingly significant problem on America’s highways, wasting time and fuel while increasing emissions.1 Most American roadways (approximately 60 percent) are already congested, and drivers spend more time traveling than ever before.2 Reducing congestion could greatly improve the quality of life and economy in the United States. Reducing the duration of incidents and thereby mitigating a significant portion of highway congestion is a key focus for traffic operation agencies. In particular, decreasing incident-detection times significantly affects the timeliness of the incident-response process.3 Because detecting incidents quickly, particularly vehicular crashes, can decrease clearance time and congestion relief time, a wide variety of detection tools are used across the United States. These tools include inductive loop detectors, side-fire radar, acoustic sensors, ultrasonic sensors and fiber optic sensors. While incident-detection tools can identify incidents using computer algorithms based on vehicular speeds, flow and density, human operators need to verify incident occurrence, frequently using other tools such as traffic cameras and hotlines such as 911. To ensure the continued efficiency of incident-management programs, many studies have examined the effectiveness of these tools, but the nature of intelligent transportation systems (ITS) involves the integration of multiple technologies that often differ between locations. It is thus difficult to compare the impact of incident-detection systems between locations to clearly compare their relative effectiveness. The time has come for a comparison of the benefits and costs of incident-detection tools as they perform at multiple sites. The objective of this study was to determine a benefit-cost ratio of the traffic sensors used in South Carolina, USA, for incident management so that incident managers and decision makers can scientifically evaluate their future use or further installation. The South Carolina Department of Transportation (SCDOT) relied upon two primary devices: loop detectors and radar sensors. Therefore, this analysis focused on those devices. Simulation of five metropolitan interstate sites allowed detailed impact analysis that other studies of tangible implementations could not offer.