Commercial trucks carry electronic control modules that record speed, braking, throttle, and hours-of-service data — often the most objective evidence of what happened in the seconds before a crash. Federal regulations also require driver logs that can reveal fatigue or hours violations.

The catch: this data can be overwritten in days or weeks as the truck keeps operating. A preservation letter sent quickly by your attorney legally obligates the carrier to retain it, which is one of the biggest reasons not to wait after a truck accident.