2 SMA ACFT COLLIDE ON TXWY. EACH CLRED TO TAXI ON THAT TXWY.

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PIPER DAKOTA ON IFR FLT PLAN WAS 'CLRED TO TAXI TO RWY 34 VIA ALPHA.' THERE ARE 2 WAYS TO GET TO ALPHA FROM AREA 3 TIEDOWN: 1) L ON ECHO TO ALPHA OR 2) R ON ECHO; L ON BRAVO; L ON RWY 12L TO ALPHA. ARROW WAS TAXIING SE ON ALPHA AT ABOUT 20-25 MPH. DAKOTA PULLED OUT OF AREA 3 AND STOPPED WHEN HE SAW ARROW. ARROW SLOWED MOMENTARILY; THEN VEERED R TO TAXI PARTIALLY ON GRASS BUT STILL HIT DAKOTA UNDER L WING AND LEADING EDGE. BOTH ACFT WERE CLRED TO TAXI ON ECHO. PLT IN ARROW SAID 'I SEE THE ACFT' BUT DID NOT STOP. I WAS INSTRUCTOR IN DAKOTA. ARROW KEPT TAXIING AS IF NOTHING HAPPENED. DAKOTA CANCELED PREVIOUS TAXI CLRNC AND TAXIED AFTER ARROW. ARROW PLT SHOULD HAVE STOPPED. BOTH ACFT WHEN COULD HAVE SHUT DOWN ENGS AND COULD HAVE BEEN PUSHED OUT OF THE WAY SO THAT 1 ACFT (AT A TIME) COULD HAVE PROCEEDED SAFELY. WHEN DAKOTA TAXIED TO RAMP NEAR ARROW; THE ARROW PLT CAME DANGEROUSLY CLOSE TO PROP TO TALK TO DAKOTA PLT. SEEMED TO BE IN A BIG HURRY. WHEN 'CONFRONTED' AFTER ENG SHUTDOWN ABOUT INCIDENT; ARROW PLT MAINTAINED HE WAS 'CLRED TO TAXI' AND THAT INCIDENT WAS NOT HIS FAULT. I ASKED THAT IF CLRED TO TAXI ALSO MEANT 'CLRED TO HIT ANOTHER ACFT.' SOLUTION?: IF YOU SEE ANOTHER ACFT ON TXWY STOP! DON'T TRY TO GAR IF OFF TXWY IF THERE IS NO ROOM. CTLR (GND ) SHOULD HAVE GIVEN SPECIFIC TAXI INSTRUCTIONS TO DAKOTA SUCH AS 'CLRED TO RWY 34 VIA L ON ECHO; R ON ALPHA.' THE WAY HE CLRED DAKOTA WAS AMBIGUOUS.