LGT TAXIED ACROSS AN ACTIVE RWY AFTER BEING TOLD TO HOLD SHORT OF IT.

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THE F/O RECEIVED A CLRNC FROM GND TO 'TAXI TO RWY 12R VIA N RAMP AND D; HOLD SHORT OF 12L.' DURING TAXI; THERE WAS A STUCK MIC AND CONSIDERABLE FREQ CONGESTION. THE CAPT STOPPED THE ACFT SHORT OF THE HOLD SHORT LINE AND WE SWITCHED TO TWR FREQ. AFTER A MOMENT OR 2; THE TWR CALLED AND ASKED IF WE HAD CLRNC TO HOLD SHORT OF 12L. AT THIS TIME; WE DETERMINED THAT WE HAD CROSSED 12L AND WERE HOLDING SHORT OF 12R AND 17. WITH THE DISTR PRODUCED BY DELAYED ENG START; TAXI CHKLIST; FREQ CONGESTION WITH NUMEROUS BLOCKED XMISSIONS; SUN IN THE FACE; AND A COMPLEX AREA OF RAMP; RWY AND TXWYS WITH RED; YELLOW AND BLACK LINES. THE CREW NEVER EVEN REALIZED THE RWY HAD BEEN CROSSED. THE COCKPIT WAS ALL BUSINESS WITH ARPT DIAGRAMS ON BOTH THE CAPT AND FO CHART CLIPS. SO; HOW DID IT HAPPEN? INATTENTION; DISTR; OR IS THE ARPT POORLY MARKED AND POORLY DESIGNED? SUPPLEMENTAL INFO FROM ACN 93840. THE DEP END RWY 12R; 17L AND 12L IS ALL 1 CONCRETE AREA; VERY CONFUSING WITH POOR MARKINGS AND CONFUSING HOLD LINES. WE TAXIED PAST RWY 12L W/O EVEN KNOWING IT. I BELIEVE THAT THIS IS ONE OF THE MOST CONFUSING GND AREAS IN THE US. I FEEL THERE SHOULD BE MUCH MORE CONSPICUOUS MARKINGS.