Context Approximately 10 million cars with automatic shoulder belt systems are
currently in use in the United States. However, reports on the effectiveness
of such restraints have yielded conflicting results.
Objective To determine the effectiveness of automatic shoulder belt systems in
reducing the risk of injury and death among front-seat passenger vehicle occupants.
Design, Setting, and Subjects Analysis of data collected from the 1993-1996 National Highway Traffic
Safety Administration Crashworthiness Data System on front-seat occupants
involved in 25,811 tow-away crashes of passenger cars, light trucks, vans,
and sport utility vehicles.
Main Outcome Measures Death and serious injury to specific body areas by use of manual lap
and shoulder belts, automatic shoulder belts with manual lap belts, or automatic
shoulder belts without lap belts, compared with no restraint use.
Results Use of automatic shoulder belts without lap belts was associated with
a decrease in the risk of death vs no restraint use but was not statistically
significant for all crashes (odds ratio [OR], 0.66; 95% confidence interval
[CI], 0.42-1.06) or for frontal crashes (OR, 0.71; 95% CI, 0.38-1.35) after
adjustment for occupant age, sex, vehicle year, airbag deployment, estimated
change in vehicle speed during the crash, and principal direction of force.
This association was significantly weaker than the 86% lower risk observed
for use of automatic shoulder belts with lap belts (OR, 0.14; 95% CI, 0.07-0.26
vs no restraint; P<.05). Use of automatic shoulder
belts without lap belts was associated with an increased risk of serious chest
(OR, 2.66; 95% CI, 1.11-6.35) and abdominal (OR, 2.06; 95% CI, 1.004-4.22)
injuries for all crashes.
Conclusions These data indicate that improperly used automatic restraint systems
may be less effective than properly used systems and are associated with an
increased risk of serious chest and abdominal injuries. Given the continued
widespread use of these automatic systems, educational programs may be warranted.