This is the estimated change in a vehicle's speed during a crash, used to describe how much force was involved in the impact.

A lot of people mistake it for the car's speed before the wreck, but it is not the same thing. A vehicle can be moving fast and still have a relatively low delta-v if the impact is minor, or moving slowly and have a higher delta-v depending on the angle and how suddenly it stops. Crash investigators, engineers, and insurance companies may calculate it from vehicle damage, scene measurements, or data pulled from an Event Data Recorder. In a claim, it often comes up when an insurer argues a crash was "too minor" to cause real injuries.

That matters because delta-v can influence disputes over causation, the seriousness of the collision, and whether medical treatment looks reasonable. In Oregon, it can also affect fault arguments under the state's comparative negligence rule: a person who is more than 50% at fault usually cannot recover damages, and any lesser share of fault reduces recovery. In side-swipe cases, parking accidents, or crashes involving oversized loads, reconstruction experts may use delta-v to challenge or support each side's version of how the impact happened. It is useful evidence, but it is only one piece of the claim and does not automatically prove how badly someone was hurt.