Are there any freeware ai cars out there that can travel along roads in fs 9 (like the ai boats on water) or are these files payware? If they're freeware can you please tell me where to get them. Thanks

Yes.
This Jag is driveable (flyable) and could be assigned to AI if one could find roads straight enough

I just use it to drive around in FS9 and look at the scenery and to drive to the airport from the hotel.

Can't remember the filename but it must be here at SimV. Search using the criteria provided.

No AI cars available that I know of but if you get some of the drivable cars it's possible to make them AI the same way the boats are. You would have to create an airport and taxiways that follow the roads then assign them to taxi around.

This is of course a resource intensive method. Less taxing on FRs would be RWY 12 or Lago FSE (like mentioned above) or you could design them as dynamic scenery. A few add on airports have that already.

These last methods are probably the best since you would have to fly very low to see cars anyway and wouldn't normally be that low except around airports. Also better selection of cars and trucks than the few available as driveable models.