B757-200 HAS RWY INCURSION AT STL.

Narrative

I WAS THE FO ON FLT FROM RFD TO STL. AFTER LNDG ON RWY 30L WE WERE TOLD BY THE TWR CTLR 'EXIT R ON TXWY E; R ON TXWY C; TAXI TO THE RAMP.' I READ BACK TO TWR; 'R ON TXWY E; R ON TXWY C THEN TAXI VIA RWY 13/31 TO THE RAMP.' THIS TAXI CLRNC REQUIRED US TO TAXI DOWN RWY 13/31; A DUAL USE RWY/TXWY. WE TAXIED VIA OUR CLRNC; AND THEN EXITED RWY/TXWY 13/31 ONTO TXWY K TO GO STRAIGHT INTO THE RAMP. PRIOR TO ENTERING THE RAMP FROM TXWY K WE WERE WAVED OFF BY ACR PERSONNEL ON THE RAMP TO ENTER THE RAMP FROM TXWY Z INSTEAD OF TXWY K. SO; WE TURNED R ON TXWY V TO PROCEED TO TXWY Z. IN SO DOING WE HAD TO REENTER THE DUAL PURPOSE RWY/TXWY 13/31 MOMENTARILY TO ENTER THE RAMP VIA TXWY Z. SINCE OUR TAXI CLRNC ONLY SPECIFIED TXWYS E AND C AND THEN TO THE RAMP; WE UNDERSTOOD IT TO MEAN THAT AFTER TXWY C WE COULD USE ANY RTE TO TAXI WITHOUT ANY FURTHER CLRNC REQUIRED. HOWEVER; WHEN WE FIRST EXITED RWY/TXWY 13/31 ONTO TXWY K; THE TWR AT SOME POINT GAVE A LEARJET CLRNC TO TKOF ON RWY 31; WHICH WE DID NOT HEAR. SO WE REENTERED RWY/TXWY 13/31. THE LEARJET SAW US AND ABORTED HIS TKOF AFTER A 1000 FT ROLL. THE CAPT AND I BOTH SAW THE LEARJET WHO WAS ONLY USING HIS SINGLE TAXI LIGHT AND MOVING TOWARD US AT TAXI SPD 2000-3000 FT E OF US ON RWY/TXWY 13/31. WE THOUGHT HE WAS ONLY TAXIING AND WE HAD CLRNC TO CONTINUE 'TO THE RAMP' AND SINCE HE WAS SLOWING EVEN MORE THAT HE WAS BEING TOLD TO WAIT FOR US ON THE OTHER (N) TWR FREQ. THE FIRST TIME WE REALIZED THE LEARJET WAS ON TKOF ROLL WAS WHEN TWR ASKED HIM WHY HE WAS ABORTING AND HE SAID DUE TO THE ACR JET. I HAVE USED THIS RWY/TXWY 13/31 NUMEROUS TIMES IN THE PAST AND HAVE NEVER SEEN IT USED AS A RWY. THUS; MY GUARD WAS DOWN. I THOUGHT IT WAS ONLY A TAXI RTE. CONTRIBUTING TO MY BELIEF OF THIS BEING A TAXI RTE IS: FIRST; IT IS TOO SMALL FOR MOST JET POWERED ACFT. SECOND; ATIS AT THE TIME OF THE INCIDENT WAS CALLING RWYS 30L AND 24 ACTIVE; NOTHING WAS SAID ABOUT RWY 31. THIRD; NO MENTION WAS MADE BY TWR OF THE STATUS OR INTENTION TO USE RWY 31 FOR TKOF. FOURTH; THE LEARJET SHOULD HAVE HAD ALL 3 OF HIS LNDG LIGHTS ON TO SIGNIFY HIS TKOF STATUS WHICH HE DID ON HIS FOLLOWING TKOF. TO PREVENT THIS FROM HAPPENING AGAIN RWY/TXWY 13/31 AND ANY SIMILAR DUAL PURPOSE RTES IN THE COUNTRY NEED TO BE USED FOR ONLY ONE PURPOSE AT ANY TIME. WHEN IN USE THIS NEEDS TO BE WELL EMPHASIZED BY CTLRS. FORTUNATELY THERE WAS NO ACCIDENT; BUT ALL THE INGREDIENTS WERE PRESENT. THIS INCIDENT TOOK PLACE AT LAMBERT ST LOUIS IAP ON AUG/XX/96 AT BB55 LCL TIME AT NIGHT.