CRJ FIRST OFFICER REPORTS TAKE OFF FROM TUS WITH C172 HOLDING DOWN FIELD ON THE RUNWAY SIDE OF THE HOLD SHORT LINE. SINGLE CONTROLLER FOR BOTH GROUND CONTROL AND LOCAL CONTROL.

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TAXIED TO RWY 29R WITH GND CTL. UPON REACHING THE HOLD SHORT LINE; CHANGED TO LCL CTL FREQ. LCL CTL (SAME CTLR) ISSUED INSTRUCTIONS TO POS AND HOLD. A C172 WAS VISIBLE TO THE R SIDE APPROX 1/3 OF THE WAY DOWN THE RWY AND APPEARED TO BE CLR; WAITING FOR TAXI INSTRUCTIONS. LCL CTL ISSUED TKOF CLRNC; AND BELIEVING THE C172 TO BE CLR; WE ADVANCED PWR AND BEGAN OUR TKOF ROLL. AS WE DREW CLOSER TO THE CESSNA AND HIS POSITION RELATIVE TO THE HOLD SHORT LINE CAME INTO VIEW; IT BECAME CLR TO ME (FO; PLT MONITORING) THAT IT WAS STOPPED WITH THE WHOLE ACFT ON THE RWY SIDE OF THE LINE. I POINTED OUT THE CESSNA'S POS TO THE CAPT (PF). SINCE THE CESSNA WAS WELL BEYOND OUR WING SPAN; FACING AWAY FROM US AND NOT MOVING; HE ELECTED TO CONTINUE THE TKOF AS THIS APPEARED TO BE THE SAFEST COURSE OF ACTION. I STATED MY SUPPORT FOR HIS DECISION. WE WERE BUSY CLEANING UP THE ACFT AND CONFIGURING THE FLT DIRECTOR IMMEDIATELY AFTER TKOF SO I DID NOT TELL LCL CTL ABOUT THE CESSNA'S POSITION UNTIL WE RECEIVED THE HDOF TO DEP CTL APPROX 15 SECONDS AFTER LIFTOFF. IN THE MEANTIME; LCL CTL ISSUED A TKOF CLRNC TO AN ACR Y FLT BEHIND US. I THEN TOLD LCL CTL THAT THE CESSNA WAS ON THE RWY; BUT THE CTLR SEEMED CONFUSED AND ASKED ME 'WHICH CESSNA; THE ONE AT ALPHA 14?' I CHKED MY ARPT PAGE (THIS TOOK PERHAPS 5 SECONDS); THEN CONFIRMED THAT THIS WAS THE CORRECT POS. AN ACR Z AIRLINES CREW; HOLDING SHORT OF THE RWY; SAID THAT THEY HAD MENTIONED IT TO GND CTL AS THEY TAXIED VIA TXWY A; PAST THE CESSNA; ON THEIR WAY TO THE RWY. LCL CTL THEN QUERIED THE CESSNA ABOUT HIS POS AND ITS PLT ADMITTED THAT HE HAD BEEN STOPPED ON THE WRONG SIDE OF THE HOLD SHORT LINE BUT THAT HE WAS NOW CLR OF THE RWY. I DON'T KNOW IF HE WAS CLR PRIOR TO THE ACR Y ACFT PASSING THE A-14 INTXN. CLEARLY; THE CAUSE OF THIS INCIDENT WAS THE CESSNA PLT'S FAILURE TO PROPERLY EXIT THE RWY PAST THE HOLD SHORT LINE; BUT IT COULD HAVE BEEN PREVENTED HAD THE CTLR MAINTAINED BETTER SURVEILLANCE OF THE AIRFIELD. HE SHOULD HAVE VISUALLY SCANNED THE RWY PRIOR TO ISSUING A TKOF CLRNC AND NOTED THE POS OF THE CESSNA. I FEEL THAT A STRONG CONTRIBUTING FACTOR WAS THE INADEQUATE STAFFING OF THE TUS ATCT AT THE TIME. A SINGLE CTLR WAS OPERATING THE GND CTL AND LCL CTL POSITIONS. HE WAS HANDLING MULTIPLE ACR TAXI REQUESTS ON GND CTL WHILE SIMULTANEOUSLY CTLING THE RWYS AND AIRSPACE ON LCL CTL. HE MISSED AN ADVISORY FROM THE ACR Z CREW ON GND CTL THAT THE CESSNA WAS ON THE RWY; AND NEITHER US NOR THE ACR Y CREW HEARD IT BECAUSE WE HAD ALREADY SWITCHED TO LCL CTL. DUE TO OUR RELATIVELY LOW SIGHT-LINE TO THE CESSNA AND THE DISTANCE FROM THE THRESHOLD TO THE A-14 INTXN; WE WERE UNABLE TO SEE THAT THE CESSNA WAS ON THE RWY UNTIL WE WERE WELL INTO OUR TKOF ROLL; SO WE ACCEPTED A TKOF CLRNC THAT SHOULD HAVE BEEN REFUSED; AS DID ACR Y. I POSSIBLY COULD HAVE PREVENTED A NEAR MISS FOR ACR Y HAD I SPOKEN UP IMMEDIATELY; BUT WE WERE AT ROTATION SPD VERY SHORTLY AFTER MAKING THE DECISION TO CONTINUE AND MY FOCUS WAS DIRECTED TO MAKING CALLOUTS FOR GEAR/FLAP RETRACTION AND RESPONDING TO THE CAPT'S REQUESTS FOR FLT DIRECTOR MODE CONFIGN. IT DIDN'T OCCUR TO ME THAT ANOTHER ACFT WAS IN JEOPARDY UNTIL I HEARD LCL CTL ISSUE ACR Y'S TKOF CLRNC. I SHOULD HAVE BEEN MORE AWARE OF THE POTENTIAL FOR A REPEATED LOSS OF SEPARATION; SINCE I KNEW THAT ACR Y HAD TAXIED RIGHT BEHIND US. UPON REFLECTION; OUR CONFIGN COULD HAVE WAITED FOR A FEW SECONDS WHILE I NOTIFIED LCL CTL OF THE CESSNA'S POS.