RIC Controller described a confused communication event between ATC and an airport vehicle working on or near an active runway during low visibility conditions.

Narrative

RIC airport was IFR with 1/4 to 1/2 mile Tower visibility; which means the controllers could not see most of the runways and taxiways. Runway 34 was the landing runway and Runway 2 was being used for departures. I relieved the CPC who was working the Ground Controller; Clearance Delivery; CIC position combined. In the briefing; he indicated that there was a vehicle working on a sign at Runway 25 and Taxiway L. I had talked to Airport Operations earlier that evening and I was aware that there was a sign out of service on the intersection of Runway 34 and Runway 25. I questioned the Controller being relieved about the position of the vehicle and he again said the vehicle was not on Runway 34. After assuming the position; I questioned the vehicle directly and the vehicle operator indicated that he was on Runway 34 and Runway 25. I instructed the vehicle to exit Runway 34 because there was traffic on an 8 mile final. Vehicle complied and there was no loss of separation. Recommendation; use standard phraseology in response to vehicle requests. Emphasize need for heightened awareness during periods of reduced visibility.