Narrative:

I was on local control-X position during marginal weather operations. Runway 34R/left was under my control and I was actively using them for mostly departure traffic. Local control-Y was open and he had control of runway 25. I instructed aircraft X to line up and wait on runway 34R; at that time the runway appeared clear. I verified this on the asde-X. I then went to runway 34L and cleared an aircraft for takeoff that was already in position. I was then notified that in a few minutes runway 34R was going to close for snow removal; and vehicles were being staged for this operation on the parallel taxiway. I returned to runway 34R and cleared aircraft X for takeoff. Aircraft X accepted the takeoff clearance; again the runway appeared clear. About 10 seconds passed and I noticed aircraft X had not moved. As I scanned the runway again; aircraft X keyed up and stated there was a vehicle on the runway moving towards them. I then canceled takeoff clearance and began to find out how and why there was a vehicle on an active runway I was using. We watched as the vehicle exited the runway. The vehicle in question turned out to be an operations airport vehicle that had made a wrong turn onto runway 34R without ATC approval. After a brief delay I began working departures off both runways again and shortly thereafter I was relieved from position. During investigation and review of ground radar replay on the asde-X it clearly showed that the airport operations data tag had ops X tagged on the display; however as the vehicle began its drive towards the runway the data tag jumped to another vehicle. This left the operations vehicle as only a small blue primary target on the ground radar. That small blue target moved ever so slowly down the runway and eventually aircraft X saw the vehicle and reported its position. During low visibility; de-icing and snow operations only one person is in the operations vehicles. This is a very busy time for them with multiple radio frequencies; computers and many times they are leading a line of 70 or more snow plows; sweepers and equipment clearing taxiways and runways of the snow and slush. During these times of increased workload; it would only make sense to have 2 people in the operations vehicles as a precaution. Also; if the operations vehicles had special transponder unique to that vehicle; the data tag most likely would not have jumped to another vehicle. Had the data tag not jumped; when the operations vehicle entered the runway he would have stayed pink in color and much larger on the screen with his data tag. This would have made it easier to see the vehicle and might have changed the outcome of this event.

Related reports:

Google
 

Original NASA ASRS Text

Title: DEN Tower Controller reported that when an air carrier aircraft was cleared for takeoff; the flight crew reported a vehicle on the runway. It was later determined to be an airport operations vehicle on the runway without clearance. ASDE-X data block jump contributed to the confusion.

Narrative: I was on Local Control-X position during marginal weather operations. Runway 34R/L was under my control and I was actively using them for mostly departure traffic. Local Control-Y was open and he had control of Runway 25. I instructed Aircraft X to line up and wait on Runway 34R; at that time the runway appeared clear. I verified this on the ASDE-X. I then went to Runway 34L and cleared an aircraft for takeoff that was already in position. I was then notified that in a few minutes Runway 34R was going to close for snow removal; and vehicles were being staged for this operation on the parallel taxiway. I returned to Runway 34R and cleared Aircraft X for takeoff. Aircraft X accepted the takeoff clearance; again the runway appeared clear. About 10 seconds passed and I noticed Aircraft X had not moved. As I scanned the runway again; Aircraft X keyed up and stated there was a vehicle on the runway moving towards them. I then canceled takeoff clearance and began to find out how and why there was a vehicle on an active runway I was using. We watched as the vehicle exited the runway. The vehicle in question turned out to be an operations airport vehicle that had made a wrong turn onto Runway 34R without ATC approval. After a brief delay I began working departures off both runways again and shortly thereafter I was relieved from position. During investigation and review of ground radar replay on the ASDE-X it clearly showed that the airport operations data tag had Ops X tagged on the display; however as the vehicle began its drive towards the runway the data tag jumped to another vehicle. This left the operations vehicle as only a small blue primary target on the ground radar. That small blue target moved ever so slowly down the runway and eventually Aircraft X saw the vehicle and reported its position. During low visibility; de-icing and snow operations only one person is in the operations vehicles. This is a very busy time for them with multiple radio frequencies; computers and many times they are leading a line of 70 or more snow plows; sweepers and equipment clearing taxiways and runways of the snow and slush. During these times of increased workload; it would only make sense to have 2 people in the operations vehicles as a precaution. Also; if the operations vehicles had special transponder unique to that vehicle; the data tag most likely would not have jumped to another vehicle. Had the data tag not jumped; when the operations vehicle entered the runway he would have stayed pink in color and much larger on the screen with his data tag. This would have made it easier to see the vehicle and might have changed the outcome of this event.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.