ACR MLG TOOK WRONG TXWY AND ENTERED ACTIVE RWY CAUSING ACFT ON APCH TO GO AROUND.

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DEPARTING ORD GATE GND CLRED US TO 'TAXI TO 14L; RIGHT TURN ON THE INNER; MORE INSTRUCTIONS ABEAM ACR B TERMINAL.' AS WE NEARED TERMINAL; I CALLED FOR MORE INSTRUCTIONS. WE WERE TOLD TO 'CONTINUE TOWARDS 9L.' AS WE NEARED THE END OF THE ACR B TERMINAL GND TOLD US 'ABEAM THE TERMINAL ALLEY TURN LEFT; THEN RIGHT ONTO 9L FOR 14L.' AS I WAS CHKING OUR POS ON THE CHARTS AND THE TXWYS THE CAPT MADE A LEFT TURN ONTO THE NEW SCENIC TXWY. I SAW A SIGN FOR RWY 9L AND ASSUMED WE WERE HEADED CORRECTLY. AS THE CAPT STARTED ONTO RWY 4L; I SAW THE 4L NUMBERS AND AN ACFT ON FINAL FOR RWY 22R. I CALLED GND AND TOLD THEM TO HAVE THE ACFT GO AROUND; THAT WE WERE ON RWY 4L. GND ANSWERED THAT THE GO AROUND WAS BEING MADE AND THAT WE SHOULD CONTINUE FOR THE OLD SENIC AND THEN TO RWY 14L. NO COMMENT FROM GND AND THE REST OF THE TAXI WAS NORMAL WITH NO OTHER PROBS. HUMAN FACTORS WERE THE MAJOR PROBS. GND ISSUED INCOMPLETE INSTRUCTIONS. I ASSUMED THAT THE CAPT; WHO HAD BEEN PREVIOUSLY BASED AT ORD FOR 18 YRS; KNEW WHERE HE WAS GOING. THE CTLR'S ASSUMPTION THAT WE KNEW AND UNDERSTOOD HIS INTENTIONS; AND THE CORRECT ROUTE TO RWY 14L. CONTRIBUTING FACTORS WERE THE USE OF 9L-27R AS A TXWY W/O ISSUING A NOTAM OR PUTTING IT ON THE ATIS; BUSY GND CTLR UNABLE TO MONITOR THE MOVEMENT OF EVERY ACFT; AND THE CONFUSION CAUSED BY THE LARGE AMOUNT OF CONSTRUCTION; TEMPORARY AND CLOSED TXWYS COVERED BY THE ATIS ANNOUNCEMENT: 'NUMEROUS TXWYS CLOSED IN THE VICINITY OF 9L-27R.' THERE MAY BE NO SINGLE SOLUTION TO THE PROB AT ORD. THE ARPT IS TERRIBLY DESIGNED AND NOT WELL LAID OUT FOR SIMPLE TAXI ROUTES. IT IS ALSO OVERCROWDED AND MADE WORSE BY CONSTRUCTION; LCL RULES AND DAILY CLOSING AND OPENING OF TAXI ROUTES. FULL TAXI INSTRUCTIONS AND COMPLETE NOTAMS AND ATIS ON TXWY/RWY USE; OPENING AND CLOSING AND TEMPORARY TXWYS WOULD HELP; AS WOULD THE FINISH OF THE CONSTRUCTION AND ADDITIONAL TXWYS/RWYS. A RELIEVER ARPT TO HANDLE CARGO FLTS AND THE USAF AIR GUARD WOULD MAKE MORE ROOM AVAILABLE FOR COMMERCIAL EXPANSION.