Seat belt use inducing systems and seat belt use counting systems were installed in fleet vehicles of the Automobile Club of Southern California. The results were: 1.Mean group seat belt use for three use inducement systems were sequencing system 77%; ignition interlock system 86%; and speed limiting interlock system 81%. 2.There was no significant change of seat belt use for any of the three inducement systems according to time of exposure. 3.There was a significant difference between previous no system seat belt use (mean 24%) and no-system seat belt after exposure to the use inducing system (mean 49%). 4.The vehicle drivers were given a questionnaire at periodic intervals, the results of which indicated higher self-reported than actual seat belt use. Also specific confusion, inconvenience and discomfort factors were identified and rated. The conclusions were: 1.use inducing systems cause a significant increase in seat belt use of fleet vehicle drivers. This increase, while probably of a different magnitude, will occur in vehicles operated by the general public. 2.No one use inducing system tested was significantly superior in increasing seat belt use than another. 3.Temporary exposure to a use inducing system appears to cause a permanent increase in the non-induced seat belt use of exposed subjects. 4.Improvement of seat belt hardware and geometry related to the human factor engineering aspects may further improve seat belt use.