Backing Acceleration & Response Time to an Audible Warning in a Field Test

Introduction

Young children are significantly over-represented in run-over backing crashes, often occurring in driveways withhigh-profile vehicles like SUVs and minivans that offer restricted rearward visibility. Statistics indicate that 80% of pedestrians struck in driveways are under age five, and many of these fatalities involve a parent driving the family vehicle. The primary purpose of this study was to develop asupplemental backing safety system by understanding real-world driver behavior, specifically backing acceleration and response times. The research evaluated four key hypotheses: 1) acceleration is lower in short versus long backing maneuvers; 2) response times are slower at the start of backing due to highcognitive demands; 3) braking latency increases alongside response times; and 4) the current industry-standard 2-meter detection range is insufficient to avoid most crashes.

Methodology

This field experiment utilized a2007 Volkswagen Touareg equipped with a rearview camera, a 4Hz sonar sensor, and an audible proximity warning system. The study recruited36 participants (28 males, 8 females) with an average of 9.3 years of driving experience. Data was collected using a Vericom 3000 accelerometer to record speed and acceleration, while a string potentiometer measured brake pedal displacement.

Participants performed 16 trials consisting ofshort backing (5 meters) andlong backing (15 meters) maneuvers on a closed parking lot. During the trials, researchers introduced three unexpected crash scenarios using a hinged plywood surrogate of afour-year-old child. Additionally, researchers remotely activated false alarms to measure driver reaction times without an actual obstacle. Analytical methods included the Wilcoxon Signed Rank Test for non-parametric distributions andcubic function modeling to determine backing acceleration profiles.

Results

The study revealed several critical findings regarding driver performance and vehicle physics:

• High Failure Rates: Alarmingly, over half of the drivers failed to respond to the backing warning. In 27 of 35 instances involving the child surrogate, driversstruck the pedestrian, with many reporting they did not hear or appreciate the warning’s purpose.
• Prolonged Response Times: The average driver response time to a backing warning was approximately2.6 seconds, which is significantly longer than typical forward-hazard reaction times. Drivers backing long distances were significantly slower (2.88s) than those backing short distances (2.09s).
• Backing Speed and Acceleration: Short backing maneuvers reached an average peak speed of2.68 mph, while long maneuvers averaged6.17 mph. Long backers exhibited significantly higher acceleration factors than short backers.
• Braking Latency: Drivers took an average of1.15 to 1.69 seconds to reach peak brake pedal displacement after the initial application.
• Inadequate Detection Ranges: The study concluded that current sensor systems, which often only detect objects within 2 meters, areinsufficient for crash avoidance. Even at low speeds (2.7 mph), the total stopping distance required is over 12 feet.

Researchers recommend an optimized detection area of6 meters (20 feet) to account for obscured visibility and average stopping distances.

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