Modeling motorcycle helmet use in Iowa: evidence from six roadside observational surveys.

This paper investigates the influence of type of roadway, weather conditions and other factors on motorcycle helmet use rates in Iowa. Using data from six statewide roadside observational surveys of motorcycle helmet use, a bivariate probit model is estimated. The applied methodological approach allows for potentially interrelated choices of motorcycle helmet use by drivers and passengers to be examined. The estimation results can enhance our understanding of other factors than state helmet laws which correlate with motorcycle rider helmet use, and the effect that the presence of a passenger has on motorcycle driver helmet use rates.