Test Procedures with Countermeasure Timing Constraints for Intersection Movement and Left Turn Assist Safety Applications

Azeredo, Philip; Tiernan, Tim; Najm, Wassim G · 2021 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This report establishes standardized test procedures with countermeasure timing constraints for Intersection Movement Assist (IMA) and Left Turn Assist (LTA) safety applications. These systems are designed to warn drivers of imminent collisions at road junctions, specifically addressing straight crossing paths (SCP) and left turn across path/opposite direction (LTAP/OD) scenarios. The research was motivated by the high frequency and cost of these intersection crashes, which account for the majority of intersection-based fatalities and comprehensive costs among light vehicles. The goal is to qualify the performance of these applications by ensuring warnings are issued when drivers benefit from them and suppressed when no threat exists, thereby minimizing nuisance alerts. The methodology involves controlled track testing for light vehicles (passenger vehicles and light-duty trucks under 10,000 pounds) under clear weather conditions. Test scenarios are derived from naturalistic driving data, crash reconstructions, and databases such as the Fatality Analysis Reporting System (FARS) and the General Estimates System (GES). The procedures define three categories of test scenarios: crash-imminent (Do-Warn), non-crash-imminent (Suppress-Warn), and false-alert (No-Warn). Vehicle kinematic parameters, including speeds and acceleration profiles, are selected to reflect real-world driving behaviors. For instance, IMA testing uses speeds of 25, 35, and 45 mph based on crash cost distributions. Warning criteria for moving vehicles were determined using Monte Carlo simulations modeling driver braking response times and deceleration levels to identify warning times that allow 90–99% of drivers to stop safely. For stopped vehicles, criteria were derived from event data recorder (EDR) analyses of crash timing. The findings provide specific quantitative boundaries for system performance. For IMA applications where the subject vehicle is initially moving, warnings are expected between 3.7–4.4 seconds (at 25 mph) and 4.0–4.9 seconds (at 35 mph) before intersection entry. For scenarios where the subject vehicle is initially stopped, warnings are triggered when the principal other vehicle’s time-to-intersection (TTI) is between 2.6 and 4.6 seconds. The report details specific test protocols, such as IMA-DW-1, where both vehicles travel at 35 mph with a TTI difference of less than 0.75 seconds, requiring a warning at 4.0–4.9 seconds. Conversely, Suppress-Warn scenarios define conditions where vehicles cross safely with sufficient time separation (e.g., 2.5–4 seconds difference), requiring no warning. Similar procedures and timing constraints are established for LTA applications. The significance of this work lies in providing a rigorous, data-driven framework for validating intersection safety technologies. By grounding test parameters in naturalistic driver behavior and crash statistics, the procedures ensure that safety applications operate within realistic timing constraints. This approach helps developers optimize warning systems to maximize crash avoidance potential while minimizing false alerts that could lead to driver distraction or disregard. The report serves as a recommendation for safety application developers and regulators, offering a standardized method to assess the efficacy of IMA and LTA systems in preventing the most common and costly intersection crashes.

Key finding

The report defines specific kinematic parameters and timing constraints for IMA and LTA test scenarios to ensure safety applications provide warnings only when drivers are unable to safely clear intersections and suppress warnings when they can.

Methodology

simulator

Provenance

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Topics

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• time to collision looming