Narrative:

Mdw was taking off on runway 31C and landing on runway 4R. We received clearance to taxi taxiway Y, taxiway P, and taxiway east to runway 31C for takeoff. I proceeded down taxiway Y, then taxiway P, and looked left to where I thought taxiway east would be, but there were numerous barricades on that taxiway. ATIS at XA53Z stated 'use caution for barricades at taxiway east and taxiway P.' I was presupposed to think that taxiway was closed, because the previous night, we got taxi clearance taxiway Y, taxiway P, taxiway G to runway 31C, which crosses runway 31R on taxiway P. I proceeded across runway 31R, and then saw only taxiway G to get to runway 31C. I looked north and saw a B737 aircraft was indeed getting through on taxiway east, and then thought the controller did in fact want us on taxiway east, and this taxiway would not have crossed runway 31R to get to runway 31C. I then realized I had crossed runway 31R without proper clearance. It was not being used for takeoff or lndgs, but it was not notamed out, and it probably could have been used. When we crossed, both I and the first officer visually and verbally confirmed the runway's path was clear in both directions, as I do crossing every runway. Just when I was going to call ground control to confirm my error, he stated 'continue on taxiway G to runway 31C, and contact tower.' we took off normally without any further problems or comments. Conclusion, I did not follow taxi instructions, and I believe I have become yet another runway incursion statistic. Contributing factors, I was influenced by the previous day's taxi route, by what I misinterped as a closed taxiway, and not querying the controller for what I thought was a simple error on his part, taxiway east, when he must have meant taxiway G. Supplemental 579683: I even wrote it down as I typically do at busy or strange airports. I began running the before takeoff checklist. As I was running the before takeoff checklist, the captain continued to taxi on taxiway P and crossed runway 31R instead of turning left onto taxiway east prior to runway 31R. After 1 min or 2, we changed over to mdw tower, were cleared for takeoff, and nobody ever said anything about our mistake. I always follow along on the communication chart page when we taxi, even at dfw, but this time I was just 'heads down' in the cockpit at the wrong time.

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Original NASA ASRS Text

Title: F100 CREW HAD A RWY INCURSION AT MDW.

Narrative: MDW WAS TAKING OFF ON RWY 31C AND LNDG ON RWY 4R. WE RECEIVED CLRNC TO TAXI TXWY Y, TXWY P, AND TXWY E TO RWY 31C FOR TKOF. I PROCEEDED DOWN TXWY Y, THEN TXWY P, AND LOOKED L TO WHERE I THOUGHT TXWY E WOULD BE, BUT THERE WERE NUMEROUS BARRICADES ON THAT TXWY. ATIS AT XA53Z STATED 'USE CAUTION FOR BARRICADES AT TXWY E AND TXWY P.' I WAS PRESUPPOSED TO THINK THAT TXWY WAS CLOSED, BECAUSE THE PREVIOUS NIGHT, WE GOT TAXI CLRNC TXWY Y, TXWY P, TXWY G TO RWY 31C, WHICH CROSSES RWY 31R ON TXWY P. I PROCEEDED ACROSS RWY 31R, AND THEN SAW ONLY TXWY G TO GET TO RWY 31C. I LOOKED N AND SAW A B737 ACFT WAS INDEED GETTING THROUGH ON TXWY E, AND THEN THOUGHT THE CTLR DID IN FACT WANT US ON TXWY E, AND THIS TXWY WOULD NOT HAVE CROSSED RWY 31R TO GET TO RWY 31C. I THEN REALIZED I HAD CROSSED RWY 31R WITHOUT PROPER CLRNC. IT WAS NOT BEING USED FOR TKOF OR LNDGS, BUT IT WAS NOT NOTAMED OUT, AND IT PROBABLY COULD HAVE BEEN USED. WHEN WE CROSSED, BOTH I AND THE FO VISUALLY AND VERBALLY CONFIRMED THE RWY'S PATH WAS CLR IN BOTH DIRECTIONS, AS I DO XING EVERY RWY. JUST WHEN I WAS GOING TO CALL GND CTL TO CONFIRM MY ERROR, HE STATED 'CONTINUE ON TXWY G TO RWY 31C, AND CONTACT TWR.' WE TOOK OFF NORMALLY WITHOUT ANY FURTHER PROBS OR COMMENTS. CONCLUSION, I DID NOT FOLLOW TAXI INSTRUCTIONS, AND I BELIEVE I HAVE BECOME YET ANOTHER RWY INCURSION STATISTIC. CONTRIBUTING FACTORS, I WAS INFLUENCED BY THE PREVIOUS DAY'S TAXI RTE, BY WHAT I MISINTERPED AS A CLOSED TXWY, AND NOT QUERYING THE CTLR FOR WHAT I THOUGHT WAS A SIMPLE ERROR ON HIS PART, TXWY E, WHEN HE MUST HAVE MEANT TXWY G. SUPPLEMENTAL 579683: I EVEN WROTE IT DOWN AS I TYPICALLY DO AT BUSY OR STRANGE ARPTS. I BEGAN RUNNING THE BEFORE TKOF CHKLIST. AS I WAS RUNNING THE BEFORE TKOF CHKLIST, THE CAPT CONTINUED TO TAXI ON TXWY P AND CROSSED RWY 31R INSTEAD OF TURNING L ONTO TXWY E PRIOR TO RWY 31R. AFTER 1 MIN OR 2, WE CHANGED OVER TO MDW TWR, WERE CLRED FOR TKOF, AND NOBODY EVER SAID ANYTHING ABOUT OUR MISTAKE. I ALWAYS FOLLOW ALONG ON THE COM CHART PAGE WHEN WE TAXI, EVEN AT DFW, BUT THIS TIME I WAS JUST 'HEADS DOWN' IN THE COCKPIT AT THE WRONG TIME.

Data retrieved from NASA's ASRS site as of July 2007 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.