UNAUTH RWY ENTRY OP BY A PA-30.

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MY PA30 WAS PARKED AT A NEW FBO RAMP ON THE S SIDE OF THE E/W RWY. ALL OTHER FBO'S ARE ON THE N SIDE OF THE RWY WHERE THE PARALLEL TXWY IS LOCATED. THERE IS NOT A PARALLEL TXWY ON THE S SIDE OF THE RWY. GND TFC FROM S RAMP MUST ACCESS THE ACTIVE RWY TO BACK TAXI. THE NEW RAMP IS DIRECTLY ADJACENT TO THE ACTIVE RWY WITH NO TXWY IN BTWN. THIS IS A NEW FACILITY AND STRANGELY LOCATED TO PLTS WHO HAVE CUSTOMARILY VISITED THIS ARPT IN THE PAST. THERE IS NEW TWR IN OP ON THE FIELD. THE TWR CTLR ALSO HANDLES GND CTL. I STARTED THE ENGS ON MY PA30/R FOR DEP EBOUND FROM COBB COUNTY-MCCOLLUM FIELD IN THE ATLANTA; GA AREA. THE ACTIVE RWY WAS RWY 27. I CONTACTED GND CTL ON THE TWR FREQ AFTER TAXIING TO THE PAINTED LINE ON THE RAMP WHICH I THOUGHT WAS THE DIVIDER BTWN THE RAMP AND THE TXWY. I RECEIVED CLRNC TO 'TAXI TO RWY 27.' AFTER LOOKING BOTH WAYS AND OBSERVING A CESSNA 310 TAXIING SLOWLY ON THE BLACKTOP WHICH WAS CLOSEST TO ME AND THE AREA I THOUGHT WAS THE TXWY; I TAXIED OUT AND TURNED E ON THIS 'TXWY' WHICH I LATER DISCOVERED WAS RWY 9/27. ANOTHER PLT CAME ON THE RADIO IN A CALM VOICE AND ASKED THE TWR OPERATOR WHAT WAS GOING ON. I SCANNED THE AREA LOOKING FOR ANYTHING UNUSUAL AND ALSO LOOKING FOR THE RWY AND OTHER TFC. I OBSERVED A SMALL ACFT ON ABOUT A 1 1/2 MI FINAL WHICH APPEARED TO BE LINED UP FOR THE STRIP ON WHICH I WAS TAXING TO THE E. THE CTLR THEN CAME ON THE RADIO SCOLDING ME FOR TAXIING ONTO AN ACTIVE RWY. I QUICKLY TURNED 180 DEGS AND TAXIED OFF THE RWY AND ONTO THE PARALLEL TXWY ON THE N SIDE OF THE RWY. THE CTLR ASKED THE APCHING ACFT TO GAR HOWEVER THIS APPARENTLY WAS PRECAUTIONARY. AS I WAS OFF THE RWY AND WELL DOWN THE TXWY BEFORE THE APCHING ACFT WOULD HAVE LANDED ON THE ACTIVE RWY. THERE WAS NO NEAR MISS AND NO IMMINENT DANGER TO ANY OF THE ACFT IN THE VICINITY. THE CTLR CLRED ME TO TAXI 'TO RWY 27.' THIS CLRNC INDICATED TO ME THAT THE CTLR SAW ME AND THAT I SHOULD PROCEED TO TAXI. I DID NOT REALIZE I WAS SITTING AT THE ENTRANCE TO THE ACTIVE RWY AND THAT I SHOULD RECEIVE A FURTHER CLRNC TO TAXI ACROSS THE ACTIVE RWY. I FEEL THE CTLR SHOULD HAVE INCLUDED HOLDING INSTRUCTIONS OR CLRNC TO CROSS THE ACTIVE RWY IN HIS INITIAL CLRNC TO ME DUE TO THE FACT I WAS ALREADY SITTING AT THE ENTRANCE TO THE RWY WHEN I RECEIVED THE CLRNC TO TAXI. S RAMP IS A NEW FACILITY AND IS LOCATED IN AN ODDLY SITUATED POS ON THE ARPT. I NOW KNOW THERE IS NO TXWY BTWN THE RAMP AND THE ACTIVE RWY. I DID NOT REALIZE THERE WAS NO TXWY PAST THE RAMP HOLDING LINE WHEN I TAXIED TO THIS POINT. I OBSERVED NO PROMINENT MARKING AT THE RWY ENTRANCE TO INFORM ME; THE PLT; THAT I WAS ABOUT TO ENTER THE RWY WHICH IS RIGHT NEXT TO THE RAMP WITHOUT A TXWY IN BTWN. THIS ARPT HAS OPERATED WITHOUT A TWR UNTIL RECENTLY. IN PRIOR OPS AT THIS ARPT THE 'RULES OF THE ROAD' AND THE 'SEE AND BE SEEN' METHODS OF OP IN ACCORDANCE WITH FAR'S HAS PREVAILED. WITH THE ADDITION OF THE CTL TWR; PLTS ARE TAUGHT TO OBEY THE CTLR. I BELIEVE THIS EVENT WAS CAUSED BY A COMBINATION OF EVENTS BEGINNING WITH: THE CTLRS ABBREVIATED CLRNC TO TAXI WITHOUT DETAILED INSTRUCTIONS REGARDING XING THE RWY; THE ABSENCE OF A PROMINENT SIGN; MARKING THE RWY ENTRANCE AT THE NEW S RAMP; MY OBSERVATION OF THE PRESENCE OF ANOTHER ACFT WHICH APPEARED TO BE TAXIING ON THE STRIP WHICH I BELIEVED TO BE THE TXWY; MY REMEMBERING THAT THIS ARPT HAS A PARALLEL TXWY EXISTING FROM THE FBO TO THE THRESHOLD OF THE RWY AND MY INITIAL BELIEF I WAS ON THIS TXWY. I APOLOGIZED FOR THE ERROR; TAXIED OFF THE RWY AND ONTO THE PARALLEL TXWY AND DEPARTED THE AREA WITHOUT FURTHER INCIDENT. NO DAMAGE WAS DONE AND NO NEAR MISS OCCURRED.