Driver Behavior in Left Turn across Path from Opposite Direction Crash and near Crash Events from SHRP2 Naturalistic Driving

Introduction Summary

The Left Turn Across Path from Opposite Direction (LTAP-OD) crash type is recognized as one of the major fatal crash types, especially for young drivers. This scenario involves a turning vehicle (the intruder) making a left turn across the path of an oncoming through vehicle (the subject driver).

The study aimed to analyze real-world LTAP-OD events to understand the behavior of the through drivers. It focused on identifying the trigger event that causes a driver to initiate an emergency response and measuring the Perception-Response Times (PRT).

The research analyzed 122 crash and near-crash events involving an LTAP-OD scenario, sourced from the Second Strategic Highway Research Program (SHRP-2) Naturalistic Database. The goal was to compare the subject driver’s actions (braking, secondary task engagement, age, and PRT) with the behavior of the turning driver.

Methodology Summary

The study utilized the SHRP-2 Naturalistic Database, which provided continuous synchronized video and vehicle telematics data from thousands of vehicles equipped with onboard data recorders.

Data Selection and Sample

The analysis focused on through-drivers’ responses in LTAP-OD events. The final analysis included 122 events (crashes and near-crashes) where the through-driver was the subject driver.

Perception-Response Time (PRT) Measurement

Perception-Response Time (PRT) was the primary dependent measure, defined as the time from the onset of the hazard to the initiation of the subject driver’s emergency response maneuver.

The PRT measurement started at the point where the intruding vehicle first started Moving Laterally or Lane Intrusion into the through driver’s lane of travel. The measurement stopped when the subject driver either:

1. Braked hard (to a threshold of $0.4~G$ or greater).
2. Initiated a significant steering maneuver.

Variables Analyzed

The dependent measure (PRT) was compared against several factors, including:

• Kinematic Factor: Time to Contact (TTC), the time remaining until the crash point.
• Driver Factors: Age, Gender, and engagement in secondary tasks (e.g., using a cell phone).
• Turning Vehicle Behavior: The turning vehicle’s speed and distance into the subject driver’s path.

Results Summary

The study’s results showed that the subject driver’s emergency response time was heavily dependent on the kinematic factor of Time to Contact (TTC).

Significant Influence: Time to Contact (TTC)

• TTC as a Predictor: Time to Contact (TTC) was found to be the only factor that significantly affected the driver’s response times (p<.001).
• Relationship: Drivers responded significantly faster when the TTC was shorter (i.e., the turning vehicle was closer to them) and significantly slower when the TTC was longer.

This strong relationship suggests that drivers use a consistent threshold for risk assessment related to time-to-collision, overriding most other influencing factors.

Non-Significant Influences

• Driver Demographics: Age and gender of the subject driver were not significant factors influencing PRT.
• Secondary Tasks: The study found that engaging in secondary tasks did not significantly change the PRT of the subject drivers.
• Braking Behavior: The vast majority of drivers (93%) used hard braking as their first response to the LTAP-OD hazard, with only 3% using steering first, and 4% using both.

The study concludes that drivers maintain a time-based expectation of safety, initiating a response only when the intruding vehicle makes the conflict imminent. This data is valuable for calibrating the reaction thresholds of automated vehicle and collision avoidance systems.

References Cited

• Attalla, S., Toxopeus, R., Kodsi, S., and Oliver, M., “Driver Response Time to Left-Turning Vehicles at Traffic Signal Controlled Intersections,” SAE Technical Paper 2018-01-0521, 2018.
• Chang, S.H., Lin, C.Y., Fung, C.P., Hwang, J.R. et al., “Driving Performance Assessment: Effects of Traffic Accident Location and Alarm Content,” Accident Analysis and Prevention 40, 2008.
• D’Addario, P., “The Effect of Cognitive Distraction,” Master’s thesis, University of Toronto, 2014.
• Dinakar, S. and Muttart, J., “Driver Behavior in Left Turn across Path from Opposite Direction Crash and near Crash Events from SHRP2 Naturalistic Driving,” SAE Technical Paper 2019-01-0414, 2019.
• Engström, J., Ljung Aust, M., and Viström, M., Effects of Cognitive Load and Anticipation on Driver Responses to a Critical Traffic Event. In Proceedings of the Human Factors and Ergonomics Society Annual Meeting (Vol. 62, No. 1, pp. 1584-1588), Los Angeles, CA: SAGE Publications, Sept. 2018.
• Lerner, N.D., Smith, H.W., Janou, K.E., and Smalley, R.J., “Driver Braking Response Times: A Review of the Literature,” NHTSA Technical Report No. DOT-VNTSC-NHTSA-95-5, 1995.
• McGehee, D.V., Mazzae, E.N., and Baldwin, S.G., “Examination of Drivers’ Collision Avoidance Behavior Using Conventional and Antilock Brake Systems on the Iowa Driving Simulator,” NHTSA Light Vehicle Antilock Brake Research Program, Task 5. National Technical Information Service, Springfield, VA, 1999.
• Muttart, J., “Influence of Age, Secondary Tasks and Other Factors on Drivers’ Swerving Responses before Crash or Near-Crash Events,” SAE Technical Paper 2015-01-1417, 2015.
• Muttart, J.W., “Quantifying Driver Response Times Based upon Research and Real-life Data,” Proceedings of the 19th International Technical Conference on the Enhanced Safety of Vehicles (ESV), Washington, D.C., 2005.
• Neale, V.L., P. M. D’Addario, T. A. Dingus, and J. M. Hankey, The 100 Car Naturalistic Driving Study: Data Acquisition and Processing, SAE Technical Paper 2005-01-0400, 2005.
• Tarko, A.P., “Driver Response Time and Decision Sight Distance,” Transportation Research Record, 2010.
• Tarko, A.P., and T. L. Stanczyk, “Effect of Intersection Geometry on Drivers’ Braking Response to Unexpected Obstacles,” Accident Analysis and Prevention, 2018.