DIRECT Operational Field Test Evaluation: Natural Use Study: Part 3: Evaluation of Driver Behavior and Measurement of Effectiveness of DIRECT Communications Technologies Based on Vehicle Tracking around Incidents

Shahine, Ghassan; Underwood, Steven Eugene · 1998 · ROSA P / University of Michigan. Intelligent Transportation Systems Research Laboratory

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Summary

This report evaluates driver behavior and the effectiveness of communications technologies used in the Driver Information Radio using Experimental Communication Technologies (DIRECT) Operational Field Test. The study aimed to determine how different radio delivery methods influenced driver awareness of traffic incidents and subsequent diversion decisions. The test was conducted on a 15-mile segment of I-75 in the Detroit area, involving 27 vehicles equipped with one of five systems: Radio Data System/Subsidiary Communications Authority (RDS/SCA), Low Power Highway Advisory Radio (LPHAR), Automatic Highway Advisory Radio (AHAR), cellular phones, or a control group with no system. Vehicle tracking systems recorded position, speed, and time to correlate actual driver behavior with incident alerts. The researchers analyzed 188 incident-related traffic messages, categorized by severity and type (crashes, weather, construction). They assessed system effectiveness using a Measure of Effectiveness (MOE) based on message reception probability and sound quality, alongside driver satisfaction ratings. The analysis focused on whether drivers diverted from their routine commute routes in response to alerts, particularly distinguishing between reactions to crashes versus construction delays. Data collection faced challenges, including hardware failures and software errors in the tracking system, which limited the dataset to 41 fully tracked incidents. Key findings indicate that drivers rarely diverted during crash incidents, with only a 6% diversion rate. However, approximately one-third of drivers diverted in response to heavy construction delays, suggesting commuters are willing to take alternate routes when the penalty for staying on the main route is high. RDS/SCA demonstrated the highest effectiveness, achieving the highest MOE (4.21), the highest diversion rate (10 out of 122 trips), and the highest driver satisfaction ratings. This success was attributed to the system’s automatic interrupt feature, broad coverage, and high sound quality. In contrast, the cellular system was the least effective (MOE of 1.3) due to low reception probability; drivers often failed to receive timely alerts because they had to manually call in, missing the incident window. LPHAR and AHAR showed moderate performance. The study concludes that RDS/SCA is the ideal technology for transmitting incident information due to its reliability, cost-effectiveness, and ability to provide timely, automatic alerts. The authors recommend standardizing traffic message formats to include incident location, queue length, and clearance time to aid driver decision-making. They also emphasize the value of vehicle tracking in evaluating ITS effectiveness, noting that while the current tracking system had limitations, it provided crucial insights into the correlation between system reliability, message timeliness, and driver behavior. Future research should focus on using RDS subcarriers for text-based messages to overcome leasing constraints.

Key finding

RDS/SCA achieved the highest measure of effectiveness and driver satisfaction, with approximately one-third of equipped drivers diverting around heavy construction incidents compared to minimal diversion rates for cellular and control systems.

Methodology

naturalistic

Sample size: 27

Provenance

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• in vehicle coaching

Information type

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• Applied Guidance: countermeasure evaluation
• Empirical Findings: observational prevalence
• Methodological Resource: dataset resource