The Effectiveness of Seat Belts in Reducing Injuries to Car Occupants

  • Published: Transport and Road Research Laboratory, TRRL LR 811, 1976
  • Authors: C.A Hobbs
  • Date Added: 01 Feb 2013
  • Last Update: 25 Oct 2016
  • Format: html


To calculate the effectiveness of seat belts.


An in-depth study of 1,126 accidents between 1974 and 1976. Accidents were included if more than one person was injured and attended the local hospital; the hospital data was matched with police reports on the collisions. There were 2,879 vehicle occupants in the sample, including 1,100 who were uninjured. Only information from front seat occupants was used. Information on the injuries was collected and coded by severity and location on the body, using the Abbreviated Injury Scale (AIS).

Key Findings:

  • 490 front seat occupants were wearing belts, 1,163 were not, and in 303 cases seat belt use was not known.

  • Of the belted occupants, 42% were uninjured compared with 28% of the unbelted occupants.

  • There was a 45% reduction in severe or life threatening injuries, which were sustained by 107 of the 1,163 unbelted occupants and 25 of the 490 belted occupants. There was a 95% certainty that the true reduction was between 65% and 13%.

  • There was a 44% reduction in injuries classed as ‘moderate’ with 261 sustained by the unbelted occupants and 62 by the belted ones. There was a 95% certainty that the true reduction lay between 58% and 42%.

  • There was no significant difference in minor injuries between the two groups.

  • Head injuries were the most common injury recorded in the sample, but there were significantly fewer head injuries coded as AIS 2 or higher among the belted occupants.

  • The rate of head injuries was 237 per 1,000 unbelted occupants to 106 per 1,000 who were belted. Usually the injury was caused by contact with the steering wheel among belted occupants or contact with the steering wheel and area around the windscreen for unbelted occupants.

  • Seat belts prevented the occupant from being ejected from the vehicle, and that just under a quarter of those thrown from the vehicle were fatally injured.