This dangerous kinematic event occurs when a vehicle occupant slides downward and forward beneath the lap belt during a crash. It happens when the seatbelt is worn too high on the abdomen or if the seat is reclined too far back. Submarining defeats the restraint system and often causes severe internal injuries as the belt crushes soft abdominal tissue instead of the pelvis.
If you recline the passenger seat that far on the highway, you're going to submarine right under the belt if we hit something.
Related terms
Seat belt
A safety harness designed to secure an occupant in a vehicle seat during a collision or sudden stop.
Lap belt
A safety restraint strap that secures only across the passenger's hips.
Passive restraint
A vehicle safety device that operates automatically without any action required by the occupant.