MD90 CAPT INADVERTENTLY TAXIED ONTO THE ACTIVE RWY EARLY IN THE MORNING DUE TO SNOW COVERING RWY; MARKINGS; AND SIGNS. HOWEVER; SINCE HE WAS 1 OF THE ONLY 2 ACFT TAXIING OUT FOR TKOF; AND THE RWY END HE HAD TAXIED ON WAS THE DEP RWY; NO CONFLICT HAD OCCURRED.

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WE WERE GIVEN TAXI INSTRUCTIONS BY ORD'S GND CTL (121.75) TO TAXI TO RWY 32R VIA TXWY B. IT WAS STILL DARK WITH SKIES STILL SNOWING AND VISIBILITY APPROX 1 MI AND SNOW AVERAGED 4 INCHES IN DEPTH. THE PLOWED SNOW DEPTH WAS GREATER THAN THE SIGNAGE MARKINGS IN THIS AREA; BUT THE TXWYS WERE NOT JUST BARELY CRUSTED WITH LIGHT SNOW. THE RESPECTIVE MARKINGS AND LIGHTS IN MOST AREAS GOING N OF 'B' BRIDGE WERE COVERED. WE WERE SWITCHED TO TWR (126.9) AND IMMEDIATELY ASKED AS TO THE LOCATION OF RWY 32R SINCE WE COULD NOT SEE ANY VISIBLE MARKINGS NOR ITS RESPECTIVE LIGHTING. WE WERE TOLD TO TAXI NBOUND ON TXWY H3. WELL; WHAT WE THOUGHT WAS 'B' PAD AND RWY 32R WAS ACTUALLY RWY 32R AND RWY 27. TWR THEN CALLED TO LET US KNOW THAT WE WERE ON THE OVERRUN TO RWY 32R. WE THEN NOTICED RWY 32R'S MIDPOINT LIGHTING AND MARKINGS; BUT ALL THE WHILE THOUGHT IT WAS 'B' PAD SINCE ALL OF THE SIGNAGE; MARKINGS AND REILS WERE COVERED AND OBSCURED AT THE DEP END. WE COULD SEE RWY 27'S THRESHOLD LIGHTING VERY CLRLY ABOUT 1/4 MI FROM US; ALL THE WHILE THINKING IT WAS RWY 32R'S LIGHTING. SNOW REMOVAL OPS WERE IN EFFECT. ALSO; THERE WAS NOT A TFC CONFLICT SINCE RWY 32R WAS BEING USED FOR DEPS. WE HAPPENED TO BE THE FIRST OF 2 ACFT OUT THIS PARTICULAR MORNING SINCE THE LAST SNOW REMOVAL IN THIS AREA WAS STILL IN OP. SINCE 'B' PAD TO THE N OF 'B' BRIDGE WAS COMPLETELY INDISCERNIBLE AS WELL AS RWY 32R'S OVERRUN AREA; SNOW REMOVAL EQUIP WAS REQUESTED BY US. TXWY H3 AND RWY 27 WAS VISIBLE VIA ITS UNCOVERED SIGNAGE AND MARKINGS BY PREVIOUS SNOW REMOVAL EQUIP. IT JUST HAD NOT GOTTEN TO RWY 32'S AND 'B' PAD'S AREA RECENT ENOUGH FOR US. SUBSEQUENT OPS WERE NORMAL.