FYI:

Just had to have a new water line installed under county gravel road (leak) and welldriller/plumber has an air-operated 4 foot mole, that works like an internal air hammer. Dug pits, with a backhoe, on both sides of road, then layed mole on a piece of channel iron (to aim it) and start the air pressure = the internal hammer "hits" harder in one direction, than the other, so if it was to get stuck, they just reverse the air flow, and it will hammer itself out backwards.

Took a good one hour to hammer under the gravel road = they said that was pretty decent time = it could have taken longer, but ground/soil (clay) was moist from previous water leak.

This procedure also got us underneath the phone line, too; so we missed that by going 4.5 feet deep under road.

Edit: they put something like 3" PVC pipe(3 sections, so 60 ft , I believe), under gravel road, then slide new 1" diameter water line inside that pipe.(easy replacement "next time")