Date: 201707
Local time of day: 0601-1200
Location: ATL.Airport, GA
Flight conditions: VMC
Light: Daylight
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower ATL
Second aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Distraction; Situational Awareness; Confusion; Workload
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Person Air Traffic Control; Person Flight Crew
When detected: Taxi
Result: Air Traffic Control Issued New Clearance; Flight Crew Rejected Takeoff
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: We were operating flight Aircraft Y. It was like a regular flight until we were asked to line up and wait on 27R/LC. Tower crossed an airplane further down the runway while we waited for our clearance. Once tower cleared us for take off; we started our take off roll. I made 80 knots call and Captain acknowledged it and few seconds later I heard Captain saying something and he sounded surprised; so I looked up and realized that there was a another aircraft (Aircraft X) further down the runway which seemed like it was moving and attempting to cross the runway. Since there is a hump on 27R; it was hard to make out at first but as we were getting closer we both realized that they are not going to stop and were in fact crossing the runway.At this time we both unanimously decided that it was best to abort the takeoff. We were reaching approximately 120 knots at this point. Captain initiated the aborted take off and I made the calls and informed the tower that we were aborting. There was silence on the frequency. We started our abort close to Juliet or Delta taxiway and we slowed down to our taxi speed by M12 and Uniform taxiway and cleared the runway at M6; which is where Aircraft X was crossing the runway. We did not hear tower clearing Aircraft X to cross the runway. However; Aircraft X inquired from tower that if they were clear to cross the runway or not but they were simply asked to go to the ground. We ran our immediate action checklist and QRH and our brakes were very hot at this time. We called maintenance and we all agreed that we needed to go back to the gate for inspection; considering it was a high speed abort. We arranged and returned to a new gate. Maintenance got on board and we got an aircraft swap and we continued with rest of our day uneventful.High Speed Abort. Brakes were very hot. It could have been a very dangerous situation.Always pay attention. Our work is very fast paced and we always have to be aware of our surroundings at all times. Don't wait for ATC instructions if it does not look right and is unsafe; always chose the conservative side and let ATC know.


Second narrative: We were cleared for takeoff and during the takeoff roll I saw Aircraft X crossing our runway. I initiated a rejected takeoff around 120 knots near taxiway Delta. ATC was immediately notified and we were at taxi speed relatively quickly. We exited the runway; made a PA to the passengers; contacted the Flight Attendant; ran the [QRH]; contacted maintenance and arranged for a gate return. Runway incursion by Aircraft X during our takeoff roll.


Synopsis: Atlanta Tower Controllers and two pilots involved reported a runway incursion because of a missed and incorrect read back.