For vehicles from 1980-2006, we would like some statistics on the
following types of vehicles:
1-  dirt bikes, trail bikes
2-  ATVs (all-terrain vehicles; these have three or more wheels and
are for off-road use)
3-  on-road motorcycles (split into dual bikes and on-road-only bikes,
if possible; this split does not need to be included, though).
4-  automobiles, passenger vehicles (This may be reported in different
ways; please include how this is defined in the database you find.)

For each of these different categories, and separated by category and
by year, we would like:
1-number of vehicles in use in the US
2-miles driven on average
3-If possible (but optional), the number of hours driven on average
Please include clear references and sources for all information.