Date: 201506
Local time of day: 1801-2400
Location: MDW.Airport, IL
Aircraft: Large Transport
Flight plan: IFR
Flight phase: Takeoff / Launch
ATC / advisory: Ground MDW; Tower MDW
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown
Second reporter function: Ground
Anomaly: Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Person Air Traffic Control; Person Flight Crew; Person Ground Personnel
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: While working on local; I coordinated a runway crossing with the ground controller so that they could cross runway 31C behind my departing traffic. While [an aircraft] was on the departure roll; several emergency vehicles crossed on the W taxiway. The Airport Surface Detection Equipment (ASDE) alarm alerted and I advised the aircraft to use caution for the vehicles downfield. The departure lifted over and prior to the crossing vehicles and continued without incident. While vehicles are practicing on the airport surface; extra care should be taken with progressive instructions and readback accuracy.


Second narrative: I was working ground control. Rescue [vehicle] and company had been issued a crossing of runway 4L and issued a hold short of runway 31C. After listening to the tapes; the readback given was to cross runway 4R and hold short of runway 31L on Whiskey. There was additional congestion in the terminal area that I was focusing on; leading to the expectation bias of hearing the wrong readback. In addition; the Rescue vehicles appeared to comply with the hold short instruction for runway 31C. From the tower it appeared they came to a complete stop at the hold short lines. The lead vehicle then keyed up and; in a questioning tone; said 'Ground; we are crossing runway 31C'. As they started talking; they almost simultaneously started to cross runway 31C. As this was happening; a [plane] had already started takeoff roll and was almost halfway down runway 31C. I immediately told them to stop; but all 4 vehicles had already crossed the hold short lines. The readback error that was missed could have prevented the runway incursion. The rescue vehicles seemed lost on the field and they still may have crossed runway 31C with a correct read back. I will be more vigilant with listening to readbacks; especially from vehicles and aircraft that are unfamiliar. I would highly suggest better training for the rescue vehicles in 2 areas:1. Radio communications with ATC. The rescue vehicles often have issues giving correct/complete readbacks on the first transmission.2. Learning the airport layout. The rescue vehicles seemed lost while they were on the field.


Synopsis: Two Controllers and a flight Crew were involved describe a runway incursion by rescue vehicles on a training mission. The lead vehicle had been instructed to cross Runway 4L and hold short of 31C; but read back cross 4R and hold short of 31L and was not corrected by the Ground Controller. The crew is at rotate speed when the vehicles are detected and the takeoff is continued.