A CPR FLT CREW AT MDW MISSED AN ACTIVE RWY HOLD SHORT LINE. THEY CLRED THE RWY AND HELD BEHIND AN ADJACENT TXWY HOLD LINE.

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WHILE TAXIING TO RWY 22R ON TXWY P AT MDW; WE CROSSED A RWY HOLD SHORT LINE WITHOUT CLRNC. WE QUICKLY REALIZED OUR MISTAKE AND REPOSITIONED THE ACFT BEHIND THE HOLD SHORT LINE ON AN ADJACENT TXWY. DUE TO THE LOCATIONS OF THE HOLD SHORT LINES AND THE HOLD RAMP; WE NEVER TAXIED ONTO THE RWY AND NO INCURSION OR LOSS OF SEPARATION OCCURRED. ATC AS UNAWARE OF OUR MISTAKE. WE RECEIVED CLRNC FROM GND TO TAXI TO RWY 22R VIA TXWYS Y AND P WITH CLRNC TO CROSS RWY 22L; AFTER TAXIING ACROSS RWY 22L ON TXWY P WE APCHED THE HOLD SHORT LINE FOR RWY 22R. I WAS THE COPLT AT THE TIME WITH THE CAPT TAXIING.LOOKED UP FROM DOING CHKLISTS AND SAW THE HOLD SHORT LINE. I DIDN'T THINK THE CAPT WAS GOING TO STOP AND I SAID THIS WAS THE HOLD SHORT LINE AND TO STOP. HE CAPT SAID THAT THE HOLD SHORT LINE WAS FURTHER UP AND KEPT GOING. I AGAIN VERBALIZED AS WE CROSSED THE HOLD SHORT LINE AND STATING THAT WE NEEDED TO STOP. AT THIS POINT THE CAPT REALIZED HIS MISTAKE AND WE WERE ABLE TO MANEUVER THE ACFT BEHIND A HOLD SHORT LINE ON TXWY N. BECAUSE OF THE CONFLUENCE OF THE TXWYS AND BECAUSE THE HOLD SHORT LINES AT MIDWAY ARE LOCATED FURTHER FROM THE RWY THAN STANDARD LINES; WE NEVER ENCROACHED UPON THE RWY. ATC WAS NEVER AWARE OF OUR MISTAKE. THE HOLD SHORT LINE ON TXWY P IS WELL DISPLAYED AND VISIBLE. THE HOLD SHORT LINES AT MDW ARE ALL LOCATED FURTHER FROM THE RWY THAN AT OTHER ARPTS BECAUSE OF THE OBLIQUE NATURE OF THE TXWYS AND RWYS. AS A CONSEQUENCE; PLTS ARE NOT USED TO HOLDING SO FAR FROM THE RWY AND DON'T EXPECT TO SEE A HOLD SHORT LINE WHERE THEY ARE. MY CAPT COULDN'T BELIEVE THE HOLD SHORT LINE WAS THAT FAR FROM THE RWY AND CONTINUED TO THE RWY WHICH WAS STILL SOME DISTANCE AHEAD. HE FELL INTO A FAMILIAR TRAP; WHERE HE EXPECTED SOMETHING TO HAPPEN. SIMILAR TO THINKING THE LNDG GEAR IS DOWN AND LOCKED BECAUSE THE GEAR HANDLE IS IN THAT POS. THERE WAS ALSO A LACK OF 'CRM' SINCE I TOLD HIM TO STOP BUT HE KEPT GOING THINKING HE WAS RIGHT. IN RETROSPECT I SHOULD HAVE STEPPED ON THE BRAKES AND STOPPED FOR HIM. BOTH OF US HAD ARPT CHART OUT FOR MIDWAY. THERE ARE 8 'RWY INCURSION HOT SPOTS' AT MDW. THE LOCATION WHERE WE MISSED THE HOLD SHORT LINE IS NOT ONE OF THEM. THIS WAS 'CRM' BREAKDOWN BTWN THE 2 PLTS. ALL MARKINGS WERE DISPLAYED AND VISIBLE. PERSONALLY MY CORRECTIVE ACTION WILL BE TO REVIEW WHERE HOLD SHORT LINES ARE AND TO BE MORE PROACTIVE WHEN BACKING UP A CAPT. THERE WAS NO FAULT WITH THE MARKINGS OR ATC. IN FACT THE SOLID-DASHED MARKINGS OF THE HOLD SHORT LINES ARE WHAT ALERTED ME TO OUR SIT.