Date: 201907
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Other Rejected Takeoff
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Workload; Communication Breakdown
Anomaly: Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: Other Takeoff roll
Result: Air Traffic Control Provided Assistance; Flight Crew Rejected Takeoff
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: After deplaning in ZZZ we were advised the ramp was closed due to lightning in the area. Approximately 15 minutes later the ramp was opened and boarding began. This put our flight on a delay. We landed on Runway XX and expected that for departure. We prepared and briefed a Runway XX departure. Runway XX is a short taxi from the gate so we asked for a wheels up time that was shortly after our expected push. I advised the FAs (Flight Attendants) of the short taxi to the runway. When we called Ground Control for taxi we were told 'Runway XY taxi via A and E'. This extra taxi length made it tight for us to make the wheels up window. During the taxi out the FO (First Officer) and I made the proper adjustments for the runway change. We also ran a before takeoff checklist. Before taxiing; we heard a Gulfstream jet ask for a wind check. During the taxi out; we believed we heard that aircraft receive taxi instructions off the runway. This built a picture in our heads of no traffic in the patterns. We reached the end of Runway XY approximately at our takeoff time for ZZZ1. We received a line up and wait clearance. The FO read it back and we entered the runway. The FO and I mistook the line-up and wait for a takeoff clearance and began the takeoff roll. Somewhere above 80kts but below 120kts; I heard Tower say 'Aircraft X stop'. I initiated a rejected takeoff. We cleared Runway XY at A and held short of E. We made a PA and then ran the rejected takeoff QRH. Tower advised us that we did not have takeoff clearance and we agreed and we were advised of a possible pilot deviation. I called the FAs to ask if everyone was okay and after hearing yes I made another PA explaining the rejected takeoff and the next steps. We taxied back to the end of Runway XY and waited approximately 35 minutes for the brakes to cool off. During this period we needed an amended flight release due to takeoff fuel. We also spoke with the Dispatcher about FOM requirements after this event. We subsequently completed the flight to ZZZ1 without incident.I believe the Swiss cheese holes began lining up with the delay due to weather. There was a pressure to get the flight back on time for arrival into ZZZ1 due to our 5 leg day. Then the unexpected runway change put pressure on us to make the takeoff time and complete the runway change items in the FMS and a new taxi checklist. We both built a 'picture' that the traffic patterns were clear of traffic. When we reached the end of Runway XY at our takeoff time we were fully expecting a takeoff clearance. Finally it is unusual for an outstation to issue line up and wait instructions. We typically have these in HUBs but it is not typical in an outstation like ZZZ. I believe all of these factors led us to believe we had been issued a takeoff clearance when we had not. As pilots; we build an image of what's happening around us in our heads. This helps keep us ahead of the airplane and the operation and allows us to operate with a higher safety margin. The image we built in our heads was incorrect. This negatively impacted us on this flight because we expected something that wasn't happening.




Synopsis: CRJ-700 Captain reported Rejected Takeoff event due to misunderstood ATC clearance.