Fatigue, Impairment & Dangerous Behavior

Key discovery categories include the ECU download (current limiter setting, calibration identifier, software version, parameter change history), the engine manufacturer’s authorized calibration database, telematics and GPS speed data for the 90 days preceding the crash, the carrier’s written speed limiter policy, all maintenance records with attention to ECU service events, fleet management software records, internal communications regarding limiter compliance, and the carrier’s pay structure.

Carrier liability depends on what the carrier knew and what it should have known. Telematics platforms record vehicle speed continuously through GPS; a carrier whose data shows a truck consistently exceeding the limiter speed has objective evidence of tampering. Carriers that use engine manufacturer fleet management software can remotely monitor ECU parameters. A carrier that does not monitor these systems despite having the capability has chosen not to look for a problem its own systems could identify.

A forensic download of the ECU reveals the current speed limiter setting, the vehicle speed history, and the calibration identifier and software version. If the carrier’s policy was 65 mph but the ECU was set to 80 mph or had no limiter active, the discrepancy is immediate evidence of tampering. The engine manufacturer maintains records of authorized calibration files for each engine serial number, so if the calibration file does not match any authorized version, the ECU has been modified.

As of July 2025, there is no federal regulation that mandates speed limiters on commercial motor vehicles. The NHTSA and FMCSA jointly proposed a speed limiter rule in September 2016 and issued supplemental rulemaking notices through 2022, but in July 2025, both agencies formally withdrew the proposed rule. The agencies cited data gaps, policy concerns, and the potential for emerging crash-avoidance technologies to achieve safety goals more effectively. However, many carriers voluntarily set speed limiters on their fleets.