Narrative:

I was told twice by the traffic management coordinator and the snow team coordinator that runway 30 was open. Aircraft X was given instructions to line up and wait on runway 30. I observed the adse-X and I did not see any targets on the runway. I was also in the middle of coordinating a closure for runway 1C due to snow removal. It was IFR and the visibility was heavily restricted. I could not see the entire runway. I could only see the first 2;000 feet of the runway at best. At no point did I observe a target or vehicle on the runway or adse-X. Aircraft X was given a departure clearance and a vector to the southwest. Aircraft Y was given instructions to line up and wait on runway 30. As I was closing runway 1C center on the adse-X; the adse-X alerted for runway 30. I did not hear exactly what it said but I am quite sure that it did not say runway 30 occupied. I thought I closed the wrong runway when I noticed an unidentified target moving towards aircraft X. The targets were merging and at merging point. When aircraft X's target moved passed the unidentified target I asked the pilot if he was still there. The pilot stated that it was close. After observing the aircraft airborne on radar and on the assigned heading; I believe I switched the aircraft to potomac approach.I have not had a chance to review the tapes or adse-X playback. I will amend this report once I have a chance to review the incident. As mentioned earlier; I was in the middle of closing the runway when the adse-X alerted. My initial assumption was I closed the wrong runway. I am aware that my requirement is to issue a cancel takeoff clearance. By the time I noticed and assessed the situation; the targets were merging and merged. There was nothing I could do. I do not know what recommendations I can make on current procedures.

Google
 

Original NASA ASRS Text

Title: IAD Tower Controller and pilot reported a near collision on the runway between the aircraft and a snow removal vehicle.

Narrative: I was told twice by the Traffic Management Coordinator and the snow team coordinator that Runway 30 was open. Aircraft X was given instructions to line up and wait on Runway 30. I observed the ADSE-X and I did not see any targets on the runway. I was also in the middle of coordinating a closure for runway 1C due to snow removal. It was IFR and the visibility was heavily restricted. I could not see the entire runway. I could only see the first 2;000 feet of the runway at best. At no point did I observe a target or vehicle on the runway or ADSE-X. Aircraft X was given a departure clearance and a vector to the southwest. Aircraft Y was given instructions to line up and wait on Runway 30. As I was closing Runway 1C center on the ADSE-X; the ADSE-X alerted for Runway 30. I did not hear exactly what it said but I am quite sure that it did not say Runway 30 occupied. I thought I closed the wrong runway when I noticed an unidentified target moving towards Aircraft X. The targets were merging and at merging point. When Aircraft X's target moved passed the unidentified target I asked the pilot if he was still there. The pilot stated that it was close. After observing the aircraft airborne on radar and on the assigned heading; I believe I switched the aircraft to Potomac Approach.I have not had a chance to review the tapes or ADSE-X playback. I will amend this report once I have a chance to review the incident. As mentioned earlier; I was in the middle of closing the runway when the ADSE-X alerted. My initial assumption was I closed the wrong runway. I am aware that my requirement is to issue a cancel takeoff clearance. By the time I noticed and assessed the situation; the targets were merging and merged. There was nothing I could do. I do not know what recommendations I can make on current procedures.

Data retrieved from NASA's ASRS site 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.