CPR CAPT OF LTT JET ACFT INADVERTENTLY TAXI ON A CLOSED RWY AT NIGHT DURING TAXI TO PARKING.

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WE WERE WORKING APCH CTL INTO SJC. WE WERE CLRED FOR A VOR APCH TO RWY 30L; SIDE-STEP TO 30R. ACCORDING TO ATIS; RWY 30L WAS CLOSED ALONG WITH SOME TAXIWAYS. TWR WAS CLOSED AT THIS TIME AND WE CANCELLED IFR WITH APCH CTL. WE THEN ANNOUNCED OUR INTENTIONS TO LAND ON RWY 30R ON THE CTAF. AFTER LNDG ON RWY 30R; WE TURNED L ON TAXIWAY G. OUR DEST WAS SJC JET CTR ON THE W SIDE OF THE ARPT. I STOPPED FOR A MOMENT TO REVIEW THE ARPT DIAGRAM SINCE I AM NOT FAMILIAR WITH THIS ARPT. I DETERMINED THAT THERE WAS NO WAY TO TAXI TO THE W SIDE WITHOUT TAXIING ON AND/OR ACROSS SOME PART OF RWY 30L. I DECIDED SINCE I HAD TO CROSS RWY 30L; I WOULD TAKE THE MOST DIRECT RTE TO MY DEST ON THE W SIDE. I TAXIED FROM TAXIWAY G; S ON RWY 30L/12R TO TAXIWAY B AND R ON B TO THE JET CTR. I WAS MET BY AN ARPT EMPLOYEE WHO WAS UPSET THAT I HAD TAXIED ON RWY 30L. I ASKED HIM HOW TO GET FROM E TO W WITHOUT XING RWY 30L. I THINK HE SAID SOMETHING ABOUT BACK TAXIING ON THE E SIDE AND XING AT B. I UNDERSTAND THAT THE NIGHTLY CLOSING WILL NOT END UNTIL DEC. I'M SURE MANY MORE PEOPLE WILL BE CONFUSED BY THIS SITUATION.