AN ACR EMB120 ENTERS AN ACTIVE RWY WITHOUT CLEARANCE. A CONFLICT WITH A DEPARTING JETSTREAM COMMUTER AIRCRAFT RESULTS.

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AT THE TIME OF INCIDENT AND IN THE WKS PRIOR; THE YUMA ARPT HAS HAD CONSTRUCTION UNDERWAY; WITH SEVERAL TXWY CLOSURES. WE CALLED FOR; RECEIVED; AND READ BACK THE FOLLOWING CLRNC: 'TAXI RWY 8 VIA TXWY L.' ALL THE OTHER TXWYS IN THE VICINITY OF THE CIVILIAN RAMP WERE CLOSED; TXWY L BEING THE ONLY TXWY LEADING TO RWY 8. TXWY L INTERSECTS RWY 8 APPROX MIDFIELD. WE RECEIVED NO CLRNC TO HOLD SHORT OF ANY RWY; PARTICULARLY RWYS INTERSECTING RWY 8. ON PREVIOUS DAYS WHEN ISSUED THE SAME CLRNC WE STOPPED AT THE INTXN OF TXWY L AND RWY 8 ONLY TO BE TOLD TO TURN ONTO THE RWY AND BACK TAXI TO THE END -- THE IMPLICATION BEING THAT SINCE ALL THE OTHER TXWYS WERE CLOSED; WE SHOULD HAVE KNOWN TO BACK TAXI TO THE END OF RWY 8 TREATING IT AS A TXWY. WE DISCUSSED THE CLRNC; AND IT WAS DECIDED THAT THE CTLR WANTED US TO TAXI ON TXWY L; AND BACK TAXI ON RWY 8 TO THE END. WE PROCEEDED AS SUCH AND WHILE TAXIING WBOUND ON RWY 8; WE APCHED THE INTXN OF RWY 8-26 AND RWY 17-35. I WAS PERFORMING THE TAXI CHKLIST; BUT VISUALLY CLRED THE AREA R OF US APCHING THE INTXN. THE CAPT VISUALLY CLRED L. WHILE XING THE RWY THE CAPT THEN OBSERVED A JETSTREAM DEPARTING RWY 35. HE EXPEDITED TO EXIT THE RWY; THE JETSTREAM WAS AIRBORNE AS IT PASSED NEARLY OVER US. ALTHOUGH THE TAXI CLRNC MAY HAVE BEEN A VALID ONE; IT WAS VAGUE; PARTICULARLY IN LIGHT OF ALL THE CONSTRUCTION; TXWY CLOSURES AND PREVIOUS CLRNCS WE HAD RECEIVED THAT WK. WITH THE VARIETY OF ACFT OPERATING AT YUMA AND ALL THE INTERSECTING RWYS I FEEL THE TAXI CLRNC COULD HAVE BEEN MORE CLR WITHOUT ADDING MUCH VERBIAGE.