Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types
General None Reported / Taken
ATC Equipment / Nav Facility / Buildings; Procedure
DFW in South flow daily runway inspections in progress.  Air Carrier X had landed Runway 17L and was taxiing via Taxiway ER restricted short of Runway 17C. Runway 17C was closed for inspection and I had depicted it as such on the ASDE-X. Immediately after I cleared  Air Carrier X to cross Runway 17C; hold short Runway 17R the pilot responded that he had red lights (RWSL) in front of him so I instructed Air Carrier X to hold short of Runway 17C and advised that I would look into it (the reason for the lights). Next; I notified the FLM of the incident and as I did so I was scanning the runway and ASDE-X display. During my scan the only thing I detected was an airport vehicle (part of the runway inspection team) proceeding southbound on Runway 17C. Even before I had finished coordinating with the FLM; Air Carrier X reported that the lights had gone out and I issued a clearance to cross Runway 17C hold short Runway 17R. The FLM called the prototype RWSL system representative at DFW and relayed the following information to me: Even when a runway is closed in ASDE-X; RWSL runway entrance lights (RELs) will illuminate if a primary target is detected proceeding down the runway at greater than 40 knots. Essentially the RWSL system considers this target as a departing aircraft even though the ASDE-X does not. The representative also told the FLM that if I had manually tagged; the primary as a vehicle; the system would not have activated. This programming logic is not acceptable. Vehicles performing runway inspections enter and exit the runway safety area repeatedly during inspections and it is not feasible to continually put data tags on them. DFW uses 5 vehicles to perform runway inspections on 7 runways every morning and just keeping them tagged would be a full time job. The RWSL should be programmed to not alert on primary targets operating on closed runways. The ASDE-X rightly didn't alert. The RWSL introduced confusion to a situation that was completely under control. A similar situation occurred at MCO this past June and the RWSL program office suggested that the airport vehicles should be restricted; by LOA; to less than 35 or 40 KTS unless the tower was going to tag the targets. Of course the system at DFW is a prototype and not identical to the system in MCO. Regardless; this type of event is not acceptable.
DFW Controller described an apparent 'Runway Status Light (RWSL)' system anomaly; noting the ASDE-X and RWSL systems should be more closely aligned.