Narrative:

Taxiing into position on runway 4L; we received takeoff clearance. As I handed control over to the first officer and glanced down at the push-to-talk switch to acknowledge takeoff clearance; I heard the first officer state concern over another aircraft. The first officer stopped the plane and as I looked up I saw an aircraft cross runway 4L on taxiway H in front of us. We were never above a taxi speed and there was never a threat of collision. I told tower we were aborting the takeoff and was told to cancel takeoff clearance. After an aircraft landed on runway 9L; we received takeoff clearance.

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Original NASA ASRS Text

Title: B737 DEP FROM ORD CLRED FOR TKOF RWY 4L; ABORTED AFTER OBSERVING TFC XING DEP RWY AT TXWY H; OPERROR RPTED.

Narrative: TAXIING INTO POS ON RWY 4L; WE RECEIVED TKOF CLRNC. AS I HANDED CTL OVER TO THE FO AND GLANCED DOWN AT THE PUSH-TO-TALK SWITCH TO ACKNOWLEDGE TKOF CLRNC; I HEARD THE FO STATE CONCERN OVER ANOTHER ACFT. THE FO STOPPED THE PLANE AND AS I LOOKED UP I SAW AN ACFT CROSS RWY 4L ON TXWY H IN FRONT OF US. WE WERE NEVER ABOVE A TAXI SPD AND THERE WAS NEVER A THREAT OF COLLISION. I TOLD TWR WE WERE ABORTING THE TKOF AND WAS TOLD TO CANCEL TKOF CLRNC. AFTER AN ACFT LANDED ON RWY 9L; WE RECEIVED TKOF CLRNC.

Data retrieved from NASA's ASRS site as of January 2009 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.