Driver responses to Turn in Path (TIP) intrusion scenario from SHRP-2 Naturalistic Database

Introduction Summary

This research focuses on the Turn in Path (TIP) crash scenario, which occurs when an intruding vehicle (Principal Other Vehicle, or POV) turns from an intersecting road to travel in the same direction as the main road driver (Subject Vehicle, or SV). This scenario is associated with a high crash risk, primarily due to the large speed difference between the POV and SV.

The study evaluated driver response behaviors in a total of 92 real-world events (91 near-crashes and one actual crash) involving SVs responding to a POV intrusion. The data was sourced from the Second Strategic Highway Research Program (SHRP-2) Naturalistic Database. The research aimed to determine the Perception-Response Times (PRT) of drivers and the factors that influence their avoidance behavior, ultimately providing a useful response time model for accident reconstructionists.

Methodology Summary

The study utilized the SHRP-2 naturalistic database, which collected synchronized videos and vehicle dynamics (telematics) from approximately 3,500 equipped vehicles over a three-year period.

Data Selection and Definition

The initial query returned 352 events, which were filtered down to 92 events based on criteria like video quality and vehicle speed. This final sample involved 91 unique drivers (46 females and 45 males).

The primary measure was the Perception-Response Time (PRT), defined as the time from the hazard’s onset threshold to the start of the driver’s response maneuver.

• PRT Start Time (Onset Threshold): This was defined as the moment the POV was near the stop bar or at an equivalent position, specifically approximately 2 meters from the road edge.
• PRT End Time (Response Onset): This was defined as the moment the Subject Vehicle (SV) started braking hard, using a threshold of 0.4 G or more (greater than 4 m/s2).

Variables Analyzed

The researchers compared the driver’s PRT against a range of factors, including driver-related factors (Age, Gender, Response Type), POV-related factors (Time to Conflict, stopped before intrusion), and environmental/infrastructural factors (Lighting, Location).

Results Summary

The analysis showed that most factors did not significantly influence driver response times, with one major exception: Time to Conflict (TTC).

Significant Factor: Time to Conflict (TTC)

The Time to Conflict (TTC) was found to be the predominant factor influencing a driver’s emergency response behavior. Drivers responded significantly faster when subjected to shorter TTC events compared to longer ones.

The relationship between PRT and TTC was found to be a significant, large positive relationship. A linear regression model showed that TTC is an accurate predictor of PRT.

The resulting regression equation, where PRT and TTC are in seconds, is:
PRT=0.9397×TTC−1.1094

In practical terms, the results suggest that drivers typically began to brake hard (0.4 G or more) approximately 1.1 seconds before the conflict point. This implies that through-drivers maintain trust in the side road vehicle’s yielding behavior until the last moment, when the conflict becomes imminent.

Non-Significant Factors

The following factors did not significantly influence driver response times for the TIP scenario in this sample: Age, Gender, Response Type (Braking only versus Braking and Steering), whether the POV started from a stop, Side of Intrusion (right or left), and Lighting (Daylight or Night-time).

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