B717 FLT CREW FAILS TO COMPREHEND THE TRISS2 RNAV DEP DEPARTING DFW AND FLIES RWY HDG.

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AT THE GATE; WE RECEIVED OUR CLRNC FROM CLRNC DELIVERY. THE ASSIGNED DEP PROC WAS THE TRISS2 DEP. THE DEP WAS LOADED INTO THE FMS; AND I REVIEWED THE DEP PROC; CHKING IT AGAINST THE PROC IN THE FMS; AND NOTING THE ALT CLRNC. I NOTICED THAT IT WAS AN RNAV DEP; BUT DIDN'T REALIZE THAT DALLAS WAS HAVING PLTS ACTUALLY FLY THE RNAV DEP PROCS FROM THE RWY; RATHER THAN ASSIGNING A HDG TO JOIN THE PROC LIKE MANY OTHER ARPTS WE FLY TO. WE TAXIED OUT TO RWY 17R; AND WERE CLRED FOR TKOF. AFTER TKOF; I FLEW RWY HDG; NOT REALIZING THAT WE WERE SUPPOSED TO FOLLOW THE RNAV PROC. WE SWITCHED OVER TO DEP CTL; AND AT ABOUT 1200 FT; THE CTLR ASKED US IF WE WERE ON THE TRISS2 DEP. WE REPLIED THAT WE THOUGHT THAT WE WERE GIVEN RWY HDG. THE CTLR TOLD US TO PROCEED DIRECT TO TRISS; WHICH WE DID; AND THE FLT PROCEEDED NORMALLY. THE EVENT OCCURRED BECAUSE NEITHER OF US REALIZED THAT DALLAS WAS ACTIVELY USING THEIR RNAV DEP PROCS FROM THE RWY. A LOT OF THE ARPTS WE FLY TO HAVE RNAV DEPS; BUT INSTEAD OF FLYING THE PROC; THEY GIVE YOU A HDG TO FLY AND THEN LATER VECTOR YOU ONTO THE DEP. IN THINKING BACK; I REALIZE THAT WHEN THE TWR CTLR CLRED US FOR TKOF; ALL THEY SAID WAS; CLRED FOR TKOF.' THEY DIDN'T ACTUALLY GIVE US A HDG LIKE WE THOUGHT.