PLTDEV WHEN BE02 MISCOPIES CALL SIGN AND TAXIES INTO POS AT AN INTXN AS AN MD80 IS ON TKOF ROLL. COMPANY ACFT AT APCH END OF RWY HAD BEEN CLRED INTO POS AND HOLD AFTER THE MD80 WAS CLRED FOR TKOF. THE MD80 ABORTED TKOF TO AVOID THE BE02.

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I WAS WORKING LCL ASSISTANT POS. DURING A HVY ARR AND DEP RUSH; WE WERE DEPARTING RWY 34R FULL LENGTH AND AT INTXN Q. LCL CLRED THE MD80 FOR TKOF AND THE BE02 ; ACR Z; AT FULL LENGTH INTO POS TO HOLD. THE OTHER BE02; ACR Y; READ BACK INTO POS AND HOLD AND WENT ONTO THE RWY IN FRONT OF THE MD80. THE MD80 ABORTED HIS TKOF WAS STOPPED BY 500- 1000 FT FROM THE BE02; ACR Y. SIMILAR CALL SIGNS ACR Y AND ACR Z. ALSO WE HAVE NO SET DEP PROCS; IE; FULL LENGTH ALL THE TIME INTXN TKOF; ALSO READ BACK ERROR WAS MADE. SUPPLEMENTAL INFO FROM ACN 374755: DURING OUR TKOF ROLL ON RWY 34R SEA ACR Y TAXIED ACROSS IN FRONT OF US AT TXWY Q CAUSING US TO ABORT THE TKOF TO AVOID A COLLISION ON THE RWY. AS FAR AS I CAN RECALL THE ACFT HAD NEVER TALKED TO TWR; DID NOT LOOK IN EITHER DIRECTION AND JUST SLOWLY TAXIED ACROSS THE ACTIVE RWY. UPON SEEING HIM CROSS THE HOLD SHORT LINE I REALIZED THAT HE WAS NOT GOING TO STOP AND IMMEDIATELY ABORTED MY TKOF. SUPPLEMENTAL INFO FROM ACN 374761: I HAD JUST MADE THE 80 KT CALLOUTS WHEN THE COPLT NOTICED AN ACFT XING IN FRONT OF US (R TO L) AT TXWY Q. ABORTED TKOF AND ADVISED TWR. QUESTIONED TWR AS TO WHO CLRED THIS ACFT TO CROSS -- TOLD THE SUPVR WAS WORKING THE PROB. NOTIFIED COMPANY OF THE ABORT.