In addition, a majority of col-lisions represented in this data set occurred on highways (60%),due to the use of mainly CHP-investigated collisions. Both the 2013NOPUS and our data set indicate that the use of DOT-complianthelmets is higher on freeways than on surface streets, leading toa lower estimate of novelty helmet use in this data set. We foundthat 3.3% of state highway-related collisions involved novelty hel-met use, while 5.2% of collisions on other roadway types involvednovelty helmet use