AN ACR FLC TAXIES ONTO RWY 5L AT PVD; THINKING THAT IT IS A TXWY.

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PVD GND CTL CLRED US TO TAXI TO RWY 5R FROM A SPOT NEAR GATE. ALTHOUGH I DON'T RECALL THE EXACT WORDS USED; THE CTLR SAID 'GIVE WAY TO A TWIN ENG ACFT TAXIING IN AT TXWY T1; TAXI TO RWY 5R (VIA TXWY T?).' I BELIEVE THE CTLR USED THE WORDS 'VIA T;' THOUGH I'M NOT SURE. WHILE HE WAS TALKING; I WAS LOOKING TO MY L TRYING TO PICK UP A VISUAL ON THE INBOUND TWIN AND ANTICIPATING THE CLRNC. WE HELD SHORT OF TXWY T1 HDG SW UNTIL THE INBOUND TWIN WAS CLR; THEN BEGAN OUR TAXI TO RWY 5R. I INCORRECTLY DIRECTED THE CAPT TO TURN L ONTO TXWY T1; THEN R ON WHAT I THOUGHT WAS A TXWY ENRTE TO THE RWY. AS WE BEGAN OUR R TURN; IT BECAME CLR TO US THAT WE WERE IN FACT ENTERING RWY 5L. I IMMEDIATELY CALLED GND; 'GND (OUR CALL SIGN);' TO WHICH THE GND CTLR IMMEDIATELY RESPONDED '(CALL SIGN) TAXI VIA RWY 5L APPROVED;' WHICH I THEN ACKNOWLEDGED. ALTHOUGH OUR TAXI CLRNC INCLUDED A CLRNC TO CROSS THE APCH END OF RWY 5L AT TXWY D; I AM CONCERNED ABOUT OUR ACCIDENTAL RWY INCURSION. I BELIEVE MY CONFUSION WAS DUE TO WORN PAINT MARKINGS ENTERING RWY 5L AT TXWY T1; A VERY NARROW RWY (75 FT); AND A PREDISPOSITION TO TAXIING OFF THE RAMP AREA ONTO THE OUTER TXWY OF SIMILAR WIDTH. AT THIS SMALL ARPT; THE 'OUTER TXWY' WAS IN FACT A RWY. THIS WAS MY FIRST TIME AT THIS ARPT. AT MY HOME BASE ARPT IN SAN JOSE; THERE IS A SIMILAR ARPT LAYOUT WITH AN OUTER TXWY. AT SAN JOSE (AS AT OTHER ARPTS); I AM FREQUENTLY TOLD TO GIVE WAY TO INBOUND ACFT ONTO THE RAMP AREA BEFORE TAXIING ONTO THE OUTER TXWY. WX WAS CLR AND TFC VERY LIGHT EARLY IN THE MORNING; SO I THINK COMPLACENCY MAY HAVE HAD A ROLE IN THIS INCIDENT AS WELL. CLOSER ATTN TO THE ARPT DIAGRAM (WHICH I HAD OUT AND ON MY YOKE CLIPBOARD) WOULD HAVE PREVENTED THIS. THERE WAS NO CONFLICT; AND THE GND CTLR SEEMED TO ANTICIPATE OUR ACTION AND REQUEST.