A B727-200 CROSSES RWY 12R WHEN TAKING A CLRNC ISSUED TO ANOTHER ACFT BESIDE THEM AT STL; MO.

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TAXIING OUT OF STL FOR DEP. ISSUED AND RECEIVED A HOLD SHORT CLRNC FOR RWY 12R; AN ACTIVE TKOF AND LNDG RWY. HOLDING SHORT #2; THEY CLRED THE #1 ACFT TO CROSS RWY 12R. WE ARE NOW #1 TO CROSS ALONG WITH ANOTHER ACFT APPROX 3 TXWYS DOWN. WE RESPONDED WITH A FULL READBACK INCLUDING CALL SIGN TO EXPEDITE ACROSS RWY 12R ALONG WITH THE OTHER ACFT HOLDING SHORT PARALLEL WITH US. STL TWR DOES THIS COMMONLY; TAXI NUMEROUS ACFT ACROSS AN ACTIVE RWY AT THE SAME TIME. AS WE PROCEEDED ACROSS RWY 12R WITH MODERATE TO EXCESSIVE PWR; THE OTHER ACFT HOLDING SHORT WAS ALSO XING. SIMULTANEOUSLY AN ACFT WAS TAXIING INTO POS BUT USING A DIFFERENT FREQ (TWR). AT ONE POINT THERE WERE 3 ACFT ON THE RWY AT THE SAME TIME; WITH ANOTHER ON SHORT FINAL; THAT ACFT EXECUTING A GAR. WHILE WE WERE HOLDING SHORT WITH THE OTHER ACFT ON A PARALLEL TXWY AWAITING OUR XING CLRNC WE RESPONDED TO A GARBLED CALL SIGN THAT INCLUDED ONE OF OUR NUMBERS BUT CLRLY STATED TO EXPEDITE THE XING. WE THOUGHT THE TWR CALLED 2 ACFT AT THE SAME TIME TO EXPEDITE ACROSS THE RWY. WE RESPONDED WITH FULL READBACK WITH NO CORRECTION FROM THE TWR. I CONFIRMED WITH THE FO WHO SAID BACK CLRED TO CROSS QUICKLY! WHICH WE DID. AFTER ARRIVING BACK AT THE DEST WE RECEIVED A CALL FROM STL TWR THAT THEY NEVER ISSUED A XING CLRNC TO US; ONLY ISSUED A CLRNC FOR THE OTHER ACFT HOLDING SHORT. WE QUESTIONED WHY THEY DIDNT CORRECT OUR READBACK. THEY SAID ONE WAS NEVER RECEIVED; THEREFORE COULD NOT CORRECT IT. WE STILL BELIEVE WE HEARD OUR NUMBER; AT LEAST PARTIALLY. FACTORS THAT LED TO THIS EVENT; OR PROCS THAT LED TO THE EVENT: 1) STL TWR AND GND USING SEPARATE FREQS TO CTL ACFT ON THE SAME ACTIVE RWY. THIS DIFFERS FROM MOST ARPTS WHERE TWR CTLS ACFT FOR TKOF; LNDG AND RWY XING. GND CTL DURING THIS INCIDENT WAS VERY BUSY WITH A LOT OF RADIO ACTIVITY. TWR CTL IS USUALLY MUCH QUIETER WHICH WOULD HELP IN THIS TYPE OF SIT. WITH LESS TALK ON THE FREQ; LISTENING TO AN IMPORTANT RWY XING CLRNC WOULD NOT GET CONFUSED WITH SOMEONE RECEIVING A CLRNC TO TAXI OUT A RAMP AREA. 2) THE FACTOR THAT DIFFERENT MAJOR TFC ARPTS CAN OPERATE IN DIFFERENT MANNERS. A STANDARDIZATION BETWEEN ARPTS ON WHO CTLS WHAT PIECE OF ASPHALT WOULD HELP TREMENDOUSLY. 3) DIFFERENT PWR OUTPUT OF RADIOS? DO NEWER ACFT HAVE GREATER SIGNAL OUTPUT THAN OLDER ACFT? I WAS FLYING A B727 AND MY XMISSION WAS COVERED BY AN ATR72. BEING MUCH NEWER TECHNOLOGY; IS HIS RADIO STRONGER AND CLEARER THAN MINE? FOOD FOR THOUGHT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CAPT THINKS STL IS TRYING TO HANDLE TOO MUCH TFC. HE FLEW THE SAME TRIP THE NEXT WEEK; BUT WAS ABOUT 2 HOURS LATE. THE REDUCED TFC MADE THE OP MUCH MORE COMFORTABLE. HE ATTRIBUTES THE RWY CONFIGN FOR MUCH OF THE CTLR WORKLOAD. SUPPLEMENTAL INFO FROM ACN 465563: WE WERE HOLDING SHORT OF RWY 12R ON RWY 6 AT APPROX XA30. AN ATR WAS ADJACENT TO US; HOLDING SHORT ON TXWY E. GND CTL CLRED AN ACFT TO CROSS RWY 12R WITHOUT DELAY. THERE WAS A B737 ONTO HOLD AT THE DEP END OF RWY 12R. AFTER THE FO ACKNOWLEDGED THE CLRNC TO CROSS; WE NOTICED A B757 PERFORMING A GAR FROM RWY 12R. AFTER WE REACHED THE OTHER SIDE OF THE RWY; TWR ASKED US IF THERE HAD BEEN SOME CONFUSION ABOUT OUR CLRNC. THE FO REPLIED; NEGATIVE; UNDERSTOOD WE WERE CLRED TO CROSS WITHOUT DELAY. AT THE SAME TIME WE CROSSED RWY 12R; THE ATR CROSSED RWY 12R AT THE SAME TIME. APPARENTLY; THE B737 COULD NOT BE CLRED FOR TKOF SINCE THERE WERE 2 ACFT ON THE RWY; XING. HENCE; THE B757; WHO WAS ON SHORT FINAL FOR RWY 12R HAD TO PERFORM THE GAR. I BELIEVE A MAIN CAUSE OF THIS SIT IS THE FACT THAT AT STL; ACFT REMAIN ON GND FREQ EVEN FOR CLRNC TO CROSS AN ACTIVE RWY. IF WE HAD BEEN ON TWR FREQ; WE WOULD HAVE HEARD THE B737 ACFT BEING CLRED ONTO THE RWY AS WELL AS THE B757 BEING CLRED TO LAND; THIS WOULD PROBABLY HAVE PREVENTED US FROM ACCEPTING THE CLRNC TO CROSS RWY 12R. AS IT TURNED OUT; THE CLRNC TO CROSS RWY 12R WAS ONLY FOR THE ATR; EVEN THOUGH WE ACKNOWLEDGED IT; APPARENTLY THE ATR WAS ACKNOWLEDGING THE CLRNC AT THE SAME TIME WE WERE; HENCE; GND CTL HAD NO IDEA WE WERE GOING TO CROSS THE RWY AT THE SAME TIME. THEREFORE; A SECONDARY CAUSE OF THIS SIT IS THE FACT THAT WHEN ONE ACFTS RADIO BLOCKS ANOTHER ACFTS RADIO XMISSION; THERE IS NO WAY OF KNOWING THIS IF THE XMISSIONS WERE SIMULTANEOUS. SUPPLEMENTAL INFO FROM ACN 465654: WE WERE UP GND CTL. HAD WE BEEN UP TWR; LIKE MOST OF THE ARPTS IN THE UNITED STATES; WE WOULD HAVE HEARD TWR CLR THE B757 TO LAND AND THE B737 TO TAKE OFF. I ALSO BELIEVE THAT TWR AND GND WERE NOT TALKING TO EACH OTHER. HAD WE NOT CROSSED RWY 12R; THE ATR STILL WOULD HAVE. I DO NOT BELIEVE THE B737 COULD HAVE TAKEN OFF EVEN IF THE ATR OR OUR FLT HAD NOT CROSSED. IT WOULD HAVE TAKEN THE B737 AT LEAST 1 - 1 1/2 MINS FOR THE B737 TO TAKE OFF. THE B757 HAD GONE AROUND WHEN WE WERE ON THE CTRLINE OF RWY 12R. I BELIEVE THE CTLRS WERE PUSHING THE TKOF AND LNDG. OUR FLT AND ATR STEPPED ON EACH OTHERS RADIO CALL. RECOMMENDATION: 1) EVERYONE SHOULD BE UP TWR FREQ WHEN XING AN ACTIVE RWY. 2) DO NOT RUSH EVERYONE OR EXPEDITE ACFT WITHOUT HAVING RECEIVED FULL 3-WAY POSITIVE READBACK.