CTLR AND PLT RPTRS DESCRIBED RWY INCURSION AT AZO DURING TAXI TO RWY 35 REQUIRING XING OF SAME RWY.

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I ISSUED CTL INSTRUCTIONS TO A SOLO STUDENT PLT ABOARD A C172 TO 'TAXI TO RWY 35' FOR VFR PATTERN WORK. NO FURTHER RESTR WAS ISSUED. WHILE ENRTE; ACFT X CROSSED RWY 35 ON TXWY C WITHOUT A CLRNC TO DO SO; RESULTING IN AN INCURSION. I CORRECTLY EXPECTED ACFT X TO HOLD SHORT OF RWY 35 ON TXWY C. THERE WAS NO CONFLICT WITH ANY OTHER ACFT DURING THIS INCURSION. IT WAS MY LATER UNDERSTANDING THAT THE STUDENT STATED THAT HE ASSUMED; SINCE NO FURTHER RESTR HAD BEEN ISSUED WITH THE INSTRUCTION TO TAXI TO RWY 35; HE UNDERSTOOD THAT HE HAD CLRNC TO CROSS THE ASSIGNED TKOF RWY. DURING THE PAST 9 MONTHS; THIS DEV MARKS THE 4TH RWY INCURSION WITH WHICH I HAVE BEEN INVOLVED -- THE THIRD DIRECTLY INVOLVING STUDENT PLT ACTIVITY; ALL 4 OCCURRING ON RWY 35 AT THE N END. AIR TFC MGMNT HAS RESPONDED REPEATEDLY TO THE LEADERSHIP OF THE FLT TRAINING PROGRAM ABOUT THE RECENT SPATE OF RWY INCURSIONS INVOLVING STUDENTS. THE INCURSIONS CONTINUE. AIR TFC MGMNT IS NOW COMPELLED TO TAKE ADDITIONAL ACTION LOCALLY TO ENSURE THAT THE CONFUSION; WHICH STILL CONTINUES WITH SOME FLT STUDENTS; IS RESOLVED. AIR TFC MGMNT HAS ORDERED; EFFECTIVE IMMEDIATELY AFTER THIS LATEST INCURSION; THAT CTLRS SHALL ISSUE DETAILED HOLD SHORT INSTRUCTIONS FOR EVERY ACFT TAXIING FROM THE RAMP TO RWY 35 SO AS TO '...HOLD SHORT OF RWY 35 ON TXWY C.' THE SHORT-TERM EFFECT OF THIS ORDER IS EXPECTED TO REMIND STUDENTS NOT TO CROSS RWY 35 WITHOUT FURTHER CLRNC. SOME CTLRS HAD PREVIOUSLY ADOPTED THIS NEW PHILOSOPHY PRIOR TO ITS MANDATE BY MGMNT. OTHERS; LIKE MYSELF; HAD NOT. IN THE INTEREST OF IMMEDIATE; SHORT-TERM; OPERATIONAL SAFETY AT ZZZ THE NEW CTL ORDER FROM AIR TFC MGMNT SOUNDS PRUDENT. HOWEVER; THE LONG-TERM EFFECT(S) OF THIS ACTION MUST BE CONSIDERED. WILL THE NEW ATC PROC AT ZZZ; ALTHOUGH WELL INTENTIONED FOR SHORT-TERM SAFETY; ACTUALLY CONTRIBUTE TO THE CURRENT NATIONAL RISE IN RWY INCURSIONS WITH EACH SUCCESSIVE GRADUATING CLASS. THE CONFUSION OF SOME STUDENTS OVER PART 91.129(I); AS SEEN BY THEIR REPEATED FAILURES TO HOLD SHORT OF ACTIVE RWYS WHEN REQUIRED; WILL NOT MAGICALLY DISAPPEAR BECAUSE ZZZ ATC IS NOW HOLDING THEM SHORT OF EVERY INTXN/SURFACE THEY REQUIRE. SUPPLEMENTAL INFO FROM ACN 687960: THE STUDENT FAILED TO HOLD SHORT OF RWY 35 AND CROSSED THE RWY WITHOUT INCIDENT. REMEDIAL TRAINING ON THE ISSUE HAS TAKEN PLACE AND THE STUDENT IS NOW FULLY AWARE OF THIS RULE. ADDING TO THE SITUATION; THE ZZZ TWR OFTEN INCLUDES THE HOLD SHORT INSTRUCTION EVEN THOUGH IT IS IMPLIED AND OTHER TIMES THEY DO NOT. THIS CAN BE CONFUSING TO THE STUDENT; ESPECIALLY IF THEY HEAR THE INSTRUCTION GIVEN WITH AND WITHOUT DURING THE SAME FLT. SUPPLEMENTAL INFO FROM ACN 687455: WAS TOLD TO TAXI TO RWY 35; I CROSSED RWY 35 BECAUSE I DID NOT HEAR TO HOLD AND AFTER I CROSSED WAS TOLD TO CONTACT MY INSTRUCTOR AND HAVE HIM CALL THE TWR. I HAD HEARD THE CTLR TELL THE ACFT BEFORE ME TO TAXI AND HOLD SHORT OF RWY 35 BUT HE DID NOT TELL ME TO HOLD THIS IS WHY I TOOK IT AS CROSS RWY 35.