A comparison of two direct-observation methods for measuring daytime safety belt use

This study compared two methods for measuring front-outboard shoulder-belt use: looking into vehicles when they stopped at a traffic control device (SVDO) and looking into vehicles as they traveled along a traffic corridor (MVDO). The reliability of the latter method has been questioned and certain surveys, such as the National Occupant Protection Use Survey (NOPUS), use both methods to estimate safety belt use. In one experiment, the methods were compared on overall belt use rates and reliability. A second experiment investigated the effect that vehicle speed had on an observer's ability to measure accurately belt use using the MVDO method. The results showed that daytime belt use rates between methods were nearly identical and inter-method reliability was quite high, indicating that front-outboard shoulder-belt use can be measured identically with either method. The second experiment showed that measurement accuracy was not affected by vehicle speeds of up to 60 mph and that overall accuracy was above 95%.