FLT CREW OF E145 TAKES OFF FROM RWY 28R AT PIT PRIOR TO RELOCATED THRESHOLD.

Narrative

GND GAVE CLRNC TO TAXI TO RWY 28R VIA TXWYS B AND B2. AT B2 WE RECEIVED CLRNC TO TAKE OFF FROM THE RELOCATED THRESHOLD. I WAS DOING THE LINE-UP CHK AND ALL I NOTICED WAS THE RWY END LIGHTS OUT MY WINDOW; SO I ASSUMED WE WERE AT THE BEGINNING OF THE RWY. AS THE CAPT STARTED TO ADD PWR; I LOOKED UP AND SAW A YELLOW TXWY LINE AND 1000 FT DOWN WAS THE RELOCATED THRESHOLD. AT THAT TIME THE TWR SAID THE THRESHOLD WAS 1000 FT FURTHER DOWN; BUT WE HAD ALREADY STARTED THE ROLL. I HAD BEEN UNSURE AS TO THE MEANING OF OUR INSTRUCTIONS. I THOUGHT THE THRESHOLD HAD BEEN RELOCATED FROM B1 TO B2 AND THAT WE WERE CLRED FOR TKOF AT THAT POINT. I DID NOT REALIZE UNTIL AFTER TKOF PWR HAD BEEN SET THAT WE WERE TO TAXI DOWN THE RWY ANOTHER 1000 FT BEFORE ADDING PWR. THE LAST TIME I WAS AT PIT; THE TWR HAD US BACK TAXI FROM B3 TO THE THRESHOLD; SO I NEVER SAW THE TAXI LINE EXTENDING FURTHER DOWN TO B2. THE ONLY REASON I RPT THIS IS BECAUSE IF PEOPLE WERE WORKING IN THE AREA BEHIND B2; THEY COULD HAVE BEEN HURT BY OUR JET BLAST. ALSO; I GUESS ATC COULD HAVE SOME CASE OF US ADDING TKOF PWR ON WHAT WAS CONSIDERED A TXWY. THIS IS A SITUATION THAT I THINK WARRANTS A SPECIFIC CHART TO SHOW PLTS WHAT HAS CHANGED ON RWY 28R AND SHOW EXACTLY WHERE THE THRESHOLD IS NOW LOCATED. ATC DID NOT SAY ANYTHING FURTHER ABOUT THE INCIDENT; BUT WHEN HE SWITCHED US TO DEP; HE DIDN'T SOUND HAPPY.