Event Data Recorder (EDR) Analysis in Commercial vs. Passenger Vehicle Collision

Overview

In a recent multi-vehicle crash involving a tractor-trailer and a passenger vehicle at a signalized intersection, Event Data Recorder (EDR) downloads from both vehicles played a critical role in determining pre-impact driver actions, vehicle dynamics, and ultimately, fault.

While physical evidence and scene documentation remain foundational to crash reconstruction, EDR data from both heavy trucks and passenger vehicles can provide objective, time-sequenced insight into driver inputs and vehicle performance immediately before and during impact.

This case highlights how EDR data from two different systems: heavy vehicle ECM data and passenger vehicle EDR data, can be used together to develop a comprehensive and defensible reconstruction.

The Incident

Location: Rural signalized intersection

Vehicles Involved: Class 8 tractor trailer (fully loaded) and mid-size passenger sedan

Impact Type: Frontal impact to the passenger vehicle with right-front overlap from the tractor

Injuries: Serious injuries to the passenger vehicle driver

The primary dispute centered on whether the tractor trailer entered the intersection on a red light, whether the passenger vehicle failed to yield, and whether either driver attempted evasive braking.

Data Acquisition: Tractor-Trailer (Heavy Vehicle ECM Data)

The tractor was equipped with an engine control module (ECM) capable of recording vehicle speed history, throttle position, brake switch status, cruise control status, engine RPM, sudden deceleration event records, and diagnostic fault codes.

Data Acquisition: Passenger Vehicle (EDR Data)

The sedan’s airbag control module recorded pre-crash speed (typically 5 seconds prior to impact), throttle position, brake pedal application, engine RPM, delta-V (longitudinal and lateral), seatbelt status, and airbag deployment timing.

Key Findings

Pre-Impact Speed: The tractor-trailer recorded a steady speed of 47 mph in a 45 mph zone with no significant deceleration until approximately 1.5 seconds before impact. The passenger vehicle recorded 38 mph five seconds prior to impact with no braking until approximately 0.8 seconds before impact.

Brake Application: The tractor trailer brake switch activated 1.5 seconds before impact with approximately 3 mph speed reduction. The passenger vehicle brake application occurred less than 1 second before impact with minimal speed reduction.

Throttle Position: The tractor throttle reduced to 0% approximately 1.6 seconds before impact. The passenger vehicle throttle remained partially applied until approximately 1 second prior to impact.

Signal Phase Analysis: By aligning EDR timestamps, intersection signal timing data, and nearby video footage, investigators determined the tractor trailer entered the intersection approximately 2.2 seconds after the light turned red for its direction of travel.

How EDR Data Helped Determine Fault

EDR and ECM data provided objective speed verification, precise brake timing, throttle input history, and measurable driver response timing. The synchronized time histories reduced reliance on subjective testimony and allowed investigators to determine right-of-way compliance and stopping distance capability.

Similarities Between Systems

Both heavy vehicle ECM systems and passenger vehicle EDR systems record pre-crash speed, brake switch status, throttle position, and are event-triggered. Both provide objective electronic evidence to supplement physical reconstruction.

Key Differences Between Systems

Heavy vehicle ECM systems may store longer speed histories, focus on engine and operational data, and may overwrite data depending on configuration. Passenger vehicle EDR systems typically record approximately five seconds of pre-impact data, focus on occupant safety systems, and airbag deployment events are typically locked and preserved.

Conclusion

In this case, EDR and ECM downloads transformed a disputed intersection collision into a data-driven reconstruction. By integrating electronic vehicle data, scene evidence, signal timing, and damage analysis, investigators provided a scientifically supported and defensible conclusion regarding fault.

As vehicle systems continue to evolve, proper acquisition and interpretation of EDR data across vehicle types remains an essential component of modern forensic crash reconstruction.