A BAE4100 COMMUTER FLT CROSSES THE HOLD SHORT LINE FOR RWY 31L WITHOUT CLRNC AT STL.

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THE INCURSION OCCURRED DURING A MAJOR STL DEP PUSH AT APPROX XA45. WE WERE CLRED BY GND TO FOLLOW A JETSTREAM 32 AND TO TAXI TO RWY 30R AND HOLD SHORT OF RWY 30L AT TXWY J. UPON REACHING RWY 30L AT TXWY J; THE J32 WAS CLRED TO CROSS RWY 30L. WE PROCEEDED TO TURN ONTO TXWY J TOWARD THE HOLD SHORT LINE AT THE INTXN OF TXWY J AND RWY 30L. WHILE ROLLING TOWARD THE LINE; GND CALLED WITH A CLRNC OF WHICH THE CAPT AND I BOTH UNDERSTOOD AS A CLRNC TO CROSS RWY 30L AND HOLD SHORT OF RWY 30R. MY READBACK WAS '(CALL SIGN) CLRED TO CROSS RWY 30L; HOLD SHORT RWY 30R.' ATC CALLED BACK INFORMING US TO HOLD SHORT OF RWY 30L; BUT WE HAD ALREADY CROSSED THE HOLD SHORT LINE. I IMMEDIATELY INFORMED GND THAT WE HAD CROSSED THE LINE. GND PROCEEDED TO CLR US ACROSS RWY 30L TAXI TO RWY 30R AND THEN INFORMED US THAT THE CLRNC WAS TO PULL UP AND HOLD SHORT OF RWY 30L AT TXWY N. NO CONFLICT OCCURRED. DURING THESE EVENTS; GND WAS NEARLY SATURATED AND IT SEEMED 1 CTLR WAS WORKING 2 FREQS. BECAUSE OF ALL THE FREQ TFC AND THE FACT THAT WE WERE ROLLING UP TO THE HOLD SHORT LINE; THE CAPT AND I MAY HAVE SIMPLY HEARD WHAT WE ANTICIPATED WE SHOULD HEAR. I WOULD RECOMMEND THAT BOTH PLTS AND CTLRS SLOW DOWN AND CONCENTRATE MORE ON VITAL COMS RATHER THAN WORRYING ABOUT BEING FAST; ESPECIALLY DURING TIMES OF HIGH FREQ TKOF. SUPPLEMENTAL INFO FROM ACN 537805: THE OTHER PLANE WAS INSTRUCTED TO TAXI ACROSS RWY 30L ENRTE TO RWY 30R. OUR PLANE WAS INSTRUCTED TO FOLLOW THE OTHER ACFT ACROSS RWY 30L AS WELL. WE WERE TO DEPART RWY 30R AS WELL. WE HAD TO QUERY GND A COUPLE TIMES TO CONFIRM WHICH RWY WE WOULD BE DEPARTING FROM 2 DIFFERENT TIMES. AFTER WE READ BACK OUR INSTRUCTIONS; THE GND CTLR SAID WE READ BACK THE INSTRUCTIONS WRONG. WE RPTED BACK THE EXACT INSTRUCTIONS TO US. WITH THE AMOUNT OF ACTIVITY; THE CTLR SEEMED TO BE A LITTLE SHORT WITH US; WITH NO PROVOCATION FROM OUR CREW. I BELIEVE TRYING TO CLR TOO MANY PLANES ACROSS THE SAME TXWY MAY HAVE BEEN A CONTRIBUTING FACTOR.