CAPT OF A CARGO DC9 FAILED TO FOLLOW TAXI INSTRUCTIONS TO TKOF RWY RESULTING IN XING THE RWY AND CAUSING TWR TO SEND ANOTHER ACFT ON FINAL AROUND.

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WHEN TAXIING OUT FOR TKOF; I MISSED THE CORRECT TURN AFTER BEING CLRED TO TAXI FOR TKOF. INSTEAD OF TURNING L ON THE CARGO RAMP; WHICH WOULD TURN INTO TXWY U (THE PARALLEL ON MY SIDE OF THE RWY); I TAXIED ONTO TXWY B AND TURNED L ONTO THE RWY; THINKING IT WAS THE PARALLEL. AS SOON AS I GOT THE NOSE OF THE ACFT UP ONTO THE RWY; I COULD SEE IT WAS A RWY; NOT A TXWY; SO I STOPPED. I TRIED TO CONTACT GND CTL/TWR BUT SINCE IT WAS A COMBINED OP (1 PERSON) HE WAS UNABLE TO BE REACHED BECAUSE HE WAS CONTINUOUSLY TALKING WITHOUT STOP FOR SEVERAL MINS. I COULD SEE AN ACFT 5 MI OR SO ON FINAL CLOSING IN. I COULDN'T BACK UP PLUS THE TXWY WAS TOO NARROW TO TURN AROUND. EVENTUALLY I REALIZED I WAS GOING TO HAVE TO TAKE ACTION ON MY OWN SINCE THE GND/TWR WAS UNAWARE OF THE SIT AND UNREACHABLE. THE QUICKEST WAY TO CLR THE RWY WAS TO PROCEED DIRECTLY ACROSS; SO I DID AS FAST AS POSSIBLE. WHEN ACROSS; I FINALLY MANAGED TO CALL TWR TO LET HIM KNOW I HAD CLRED THE RWY AND WHY. HIS RESPONSE WAS TO SEND THE OTHER AIRPLANE ON FINAL AROUND. NEITHER THE FO NOR MYSELF RECALL SEEING A LIGHTED RED RWY SIGN PRIOR TO ENTERING THE RWY.