DAY CTLR DESCRIBED NEAR RWY INCURSION WHEN VISUAL MEMORY CUES WERE IN PLACE BUT NOT OBSERVED BECAUSE OF THE CTLR'S LOCATION IN THE TWR CAB.

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I WAS WORKING ALL TWR POS COMBINED AT THE TIME AND HAD BEEN ON POS FOR ABOUT 1 HR. I HAD 1 VEHICLE; A SNOW BLOWER; DOING TURNAROUNDS AT TXWY AND RWY INTXNS REMOVING SNOW. I HELD HIM SHORT OF THE RWY TO ALLOW SEVERAL ARRS TO LAND. ONCE THEY LANDED; I APPROVED TURNAROUNDS ON THE RWY TILL TOLD OTHERWISE. I THEN PLACED OUR MEMORY JOGGER IN PLACE TO INDICATE A VEHICLE ON THE RWY. I THEN WENT OVER TO FLT DATA TO MAKE AN ATIS. WHILE DOING THIS; I HAD 2 ACFT CALL ME TO LAND; I HAD MY HEADSET ON AND WAS ABLE TO CLR THEM TO LAND WITHOUT GOING BACK TO THE LCL CTL POS. I SCANNED THE RWY. NOT SEEING ANYONE ON THE RWY; I CLRED BOTH ACFT TO LAND. I THEN FINISHED THE ATIS AND IT WAS A RATHER LONG ONE DUE TO THE NOTAMS FOR RWY CLOSURES AND FIELD CONDITIONS THAT HAD TO BE ON THE ATIS. WHEN I RETURNED TO THE LCL/TWR POS; I REALIZED WHAT I HAD DONE. I IMMEDIATELY CONFIRMED THE VEHICLE WAS HOLDING SHORT OF THE RWY BEFORE MY NEXT ARR. WHILE THE VEHICLE NEVER ENTERED THE RWY WHILE ACFT WERE LNDG; THE POTENTIAL EXISTED FOR HIM TO BE THERE. THANKS TO AN ALERT DRIVER THAT DID NOT HAPPEN. LESSON LEARNED FOR ME WAS: NO MORE OPEN-ENDED CLRNC FOR TURNAROUNDS AND DON'T WORK THE POS IN A WAY YOU'RE NOT USED TO; IE; USE ALL YOUR TOOLS. I LIKE TO USE THE PODIUM WE HAVE FOR THE LCL CTL POS. THE PERSON I RELIEVED DID NOT; AND I DID NOT REPLACE IT AFTER I RELIEVED HIM. I BELIEVE IF I HAD BEEN USING THE PODIUM THE MEMORY JOGGER WOULD HAVE STOOD OUT MORE AND I WOULD HAVE REALIZED WHAT I WAS DOING AND CORRECTED IT BEFORE IT HAPPENED.