AN ACR LGT CREW TAXIED ONTO AN ACTIVE RWY AT NIGHT AT ORD.

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ACR FLT X GOING TO OAK WAS PUSHED BACK FROM GATE Y AT ORD. AT THE END OF THE PUSH; WE WERE HDG APPROX NE. GND CTL INSTRUCTIONS WERE TO TAXI FOR A 32L T1 TKOF VIA BRAVO N; OUTER; HOLD SHORT OF T12 FOR FURTHER INSTRUCTIONS. AS I STARTED TO TAXI; I LOOKED OVER MY L SHOULDER AND THOUGHT I WAS LOOKING DOWN THE INNER TAXIWAY. I LOOKED AHEAD AND SLIGHTLY TO THE R AND SAW THE SHORT WOLF ROAD TAXIWAY AND MISINTERPRETED THIS TO BE THE LAST ISLAND TURN-AROUND TO GET ON THE OUTER. I WAS HALFWAY AROUND THE TURN WHEN I REALIZED I HAD TURNED ON TO THE 9L-27R RWY; WHICH WAS AN ACTIVE RWY AT THE TIME. AT THE SAME TIME; I TOLD MY FO TO TELL GND CTL OF THE ERROR WE MADE; GND CTL CALLED AND ASKED IF WE KNEW WE HAD JUST TURNED ON TO AN ACTIVE RWY. I LOOKED TO THE END OF THE RWY AND COULD SEE THE LIGHTS OF AN ACFT IN TKOF POS; SO WE IMMEDIATELY CLRED THE RWY AT THE HIGHSPD TURNOFF AND TAXIED DOWN THE OUTER AS PER GND CTL'S INSTRUCTIONS. THE BAL OF THE FLT WAS NORMAL. THE RESPONSIBILITY FOR THE ERROR WAS MINE; HOWEVER; IN RETROSPECT; SOME OF THE FACTORS THAT COULD HAVE PREVENTED THIS ERROR WERE: HAVE A CLR PICTURE IN MIND OF WHERE YOU ARE AND WHERE YOU ARE GOING; ESPECIALLY AT NIGHT. I THOUGHT I DID; BUT OBVIOUSLY I DID NOT. WHEN I SAW WOLF ROAD TAXIWAY IT SHOULD HAVE TRIGGERED TO ME SOMETHING WAS NOT RIGHT. OBVIOUSLY; IT DID NOT. THE CTLRS AT ORD ARE USUALLY SO SHARP THAT NORMALLY; IF IT LOOKS LIKE YOU MAY GO IN THE WRONG DIRECTION; THEY CATCH IT IMMEDIATELY. OBVIOUSLY; FOR SOME REASON; THIS TIME HE DID NOT. EVEN THOUGH THE FO HAS FUNCTIONS TO PERFORM SUCH AS GETTING LOAD PLAN INFO AND MAKING CORRECTIONS TO THE CDU; HE SHOULD NOT LET IT KEEP HIS HEAD IN THE COCKPIT TO THE EXTENT THAT HE DOES NOT KNOW WHERE HE IS AT ALL TIMES AND KEEP THE CAPT INFORMED OF ANYTHING HE THINKS IS AMISS. OBVIOUSLY; THIS TIME HE DID NOT. SUPPLEMENTAL INFO FROM ACN 224607: THE CAPT TURNED ONTO AN ACTIVE RWY. I ASKED THE CAPT WHY HE TURNED AS HE DID; AND HE SAID THAT HE THOUGHT HE WAS PULLING AWAY FROM ANOTHER CONCOURSE. WE WERE ANTICIPATING A SHORT TAXI; AND I HAD MY HEAD IN THE COCKPIT WORKING ACARS AND PROGRAMMING COMPUTERS.