Right about here.

Gunther turned off the Mare Vaporum road and began laying tracks over virgin soil.  "You've left your prescheduled route," the truck said.  "Deviations from schedule may only be made with the recorded permission of your dispatcher."

"Yeah, well."  Gunther's voice seemed loud in his helmet, the only physical sound in a babel of ghosts.  He'd left the cabin unpressurized, and the insulated layers of his suit stilled even the conduction rumbling from the treads.  "You and I both know that so long as I don't fall too far behind schedule, Beth Hamilton isn't going to care if I stray a little in between."

"You have exceeded this unit's linguistic capabilities."

"That's okay, don't let it bother you."  Deftly he tied down the send switch on the truck radio with a twist of wire.  The voices in his head abruptly died.  He was completely isolated now.

"You said you wouldn't do that again."  The words, broadcast directly  to his trance chip, sounded as deep and resonant as the voice of God.  "Generation Five policy expressly requires that all drivers maintain constant radio--"

"Don't whine.  It's unattractive."

"You have exceeded this unit's linguistic--"

"Oh, shut up."  Gunther ran a finger over the topographical maps, tracing the course he'd plotted the night before:  Thirty kilometers over cherry soil, terrain no human or machine had ever crossed before, and then north on Murchison road.  With luck he might even manage to be at Chatterjee early.

He drove into the lunar plain.  Rocks sailed by to either side.  Ahead, the mountains grew imperceptibly.  Save for the treadmarks dwindling behind him, there was nothing from horizon to horizon to show that humanity had ever existed.  The silence was perfect.