A COMMERCIAL INST PLT FLYING A PA28 AT RDG MISUNDERSTANDS THE TAXI INSTRUCTIONS ISSUED BY GND CTL RESULTING IN A RWY INCURSION.

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AT READING; PA; ARPT; ATIS INFO INDICATED THAT RWY 31 WAS IN USE; BUT OTHER RWYS COULD BE ASSIGNED. SINCE MY DEST (PTW) WAS ONLY APPROX 20 MI TO THE SE (A 130 DEG BEARING FROM RDG); I REQUESTED FROM GND A TAXI TO RWY 13 IF AVAILABLE. THE CTLR RESPONDED WITH '...TAXI TO RWY 13.' I WAS LOCATED ON THE N RAMP. I HAD A COMMERCIAL ARPT DIAGRAM (OPPOSITE THE ILS RWY 36 APCH) WHICH INDICATED THAT I WOULD HAVE TO CROSS RWY 31/13 TO GET TO THE DEP END OF THE RWY. AT A GLANCE; I THOUGHT THAT TXWY C WOULD TAKE ME ALL THE WAY TO THE DEP END OF THE RWY. SINCE NO 'HOLD SHORT' INSTRUCTIONS WERE GIVEN; I ELECTED TO PROCEED IN THIS MANNER. UPON APCHING RWY 31/13 ON TXWY C; I OBSERVED A KING AIR DEPARTING RWY 31 TO MY L; SO I IMMEDIATELY HIT THE BRAKES; BEFORE THE RWY; BUT AFTER THE HOLD SHORT MARKINGS. THE KING AIR LIFTED OFF GREATER THAN 2000 FT PRIOR TO MY LOCATION AND PASSED OVERHEAD AT 300-500 PLUS FT; AND I THEN PROCEEDED TO CROSS THE RWY. ONCE ACROSS; I OBSERVED THE MARKINGS THAT SHOWED ME THE ASSUMED CONTINUATION OF TXWY C WAS IN FACT AN ARPT SVC ROAD WITH A STOP SIGN AT THE END. AT THAT TIME; WHILE CLR OF THE RWY AND ON THE ACCESS ROAD; THE CTLR CALLED AND ASKED '...WHAT ARE YOU DOING?' AFTER A BRIEF DISCUSSION I WAS CLRED TO CONTINUE MY TAXI TO RWY 13 AT MY DISCRETION.