Sales tax doesn't go toward roads.  There is a gasoline tax for that.  However, it has not kept up with inflation AND there are a lot more miles of pavement than there were in the 60's (new roads and added lanes to existing roads).  As a state, Colorado doesn't tax gasoline nearly as much as surrounding states; Utah, for example, has a smaller population than Colorado but an equivalent amount of road/mileage while taxing at a higher rate in order to keep them repaired.   Even though they are a very Republican voting state, they've made the conscious decision to take care of their roads and understand that it doesn't come cheap or free.  Colorado voters, partly due to TABOR and its ramifications and psychological effects, always seem to want the best of both worlds, public services (like roads and schools) but low or no taxes, regardless of political affiliation (but the low or no taxes is a Republican leaning ideology).