1. The boat underran the bridge.

2. The front and rear underrun protections can effectively protect passenger cars from inserting under trucks, rational energy absorption characteristics can improve impact compatibility.

3. An underrun protection device installed at the bottom rear-end of truck is presented.

4. Therefore, the research on collision characteristics of motor vehicles and trailers rear underrun protection for improving the safety performance of automobile collision is of great significance.

5. The results of both real vehicle crash tests and LS-DYNA simulations show that the protection device, though simple, can effectively protect car occupants in underrun accidents.

6. The simulated high head with large vertical velocity of gravity-current, the large velocity of underrun and the dense isentropes in the front are closely consistent with those observed.