AUTOMATIC VS MANUAL SAFETY BELT SYSTEMS: A COMPARISON USING STATE ACCIDENT DATA INVOLVING 1975-1979 MODEL VW RABBITS

The primary objective of this research is to assess the (A+K)-injury reducing potential of the VW Rabbit automatic shoulder belt/knee bolster system using data consisting of 10,336 accidents involving VW Rabbits during the period 1975-1979 in New York, North Carolina, Maryland, Colorado, Alabama, and South Carolina. The analysis generally involved the following: (1) investigation of potential biases arising from missing belt usage cases; (2) identifying confounding variables by variable screening and then smoothing the data using weighted least squares procedures for categorical data; and (3) examination of the components of the overall (A+K)-injury rate reduction, namely components due to usage rate differences, belt system differences, and sample variation. For the primary analyses (NY, NC, MD, and CO), the range of usage rates was 16.6% to 41.6% for manual belts versus 43.1% to 73.7% for automatic belts. Occupants in automatic belt Rabbits experienced 20 to 30 percent fewer (A+K)-injuries than their counterparts in Rabbits with conventional 3-point belt systems. The overriding factor for this reduction was the increase (at least two-fold) in the belt usage rates in automatic belt Rabbits. When used, the two belt systems are equally effective in preventing serious injuries. Although there is some variability in the results across states due to differences in reporting thresholds, variable differences, missing data rates, police reporting errors, etc., the reasonable consistency of the results between states suggests a reasonable adequacy of state accident data in addressing a question such as posed herein. In point of fact, alternative data is not yet available.