JS41 CREW WENT OFF THE FAR END OF THE RWY AFTER NIL BRAKING WAS EXPERIENCED.

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THE CAPT WAS THE PF FROM BWI TO ZZZ. ATIS RPTED 1500 FT OVCST; 3 MI VISIBILITY WITH LIGHT ICE PELLETS AND MIST. A DASH 8 LNDG BEFORE US RPTED BRAKING ACTION FAIR. WE WERE ON THE ILS RWY 5. THE CAPT LANDED ON SPD AT VREF FOR ICING CONDITIONS AND IN THE TOUCHDOWN ZONE. ON ROLLOUT; HE WAS UNABLE TO RELEASE THE FLT IDLE GATE AND MOVE THE PWR LEVERS TO GND RANGE IDLE AND REVERSE. THE CAPT BEGAN TO SLOW THE PLANE WITH TOE BRAKES AND ANNOUNCED THAT HE COULD NOT GET THE PWR LEVERS BEHIND THE GATE. AS THE ROLLOUT CONTINUED; THE PLANE SLOWED AND IT APPEARED WE WOULD BE ABLE TO EXIT THE RWY AFTER A LONG ROLLOUT. SUBSEQUENTLY; THE BRAKING ACTION BEGAN TO WORSEN AND THE ANTI-SKID LIGHT MOMENTARILY WAS COMING ON. HE ALSO WAS HAVING PROBS WITH POSITIVE CTL OVER NOSEWHEEL STEERING. WE BOTH TRIED SEVERAL TIMES TO PULL THE RELEASE AND MOVE THE PWR LEVERS TO GND RANGE AND REVERSE BUT THEY WERE JAMMED. THE PROB WAS RELAYED TO THE TWR. WE WERE GRADUALLY DECELERATING BUT SINCE NOT SURE OF OUR BRAKING OR NOSEWHEEL STEERING; WE RPTED WE WOULD BE STOPPING ON THE RWY. AS THE END OF THE RWY NEARED; IT BECAME OBVIOUS THAT OUR MOMENTUM WAS NOT GOING TO LET US SLOW ENOUGH TO TURN ONTO A TXWY OR STOP ON THE RWY. AT FLT IDLE; THE ENGS WERE STILL PRODUCING MORE FORWARD THRUST THAN THE REDUCED BRAKING COULD HANDLE. AN EMER WAS DECLARED AND WE ASKED THEM TO SEND OUT THE EMER EQUIP AS WE WERE GOING TO GO OFF THE END OF THE RWY. THE CAPT STEERED L TO CLR THE APCH LIGHTS FOR RWY 23. WE RAN OFF INTO THE FIELD AND NOSEWHEEL STEERING WAS TURNED SHARPLY TO THE L TO FORCE THE ACFT TO A STOP BEFORE FURTHER ACCELERATING DOWN AN INCLINE TOWARD A DITCH AHEAD. WE THEN COORDINATED WITH GND CTL AND OPS; AS WELL AS THE EMER TEAM THAT CAME OUT TO THE ACFT TO SECURE TRANSPORTATION FOR THE PAX BACK TO THE TERMINAL. THERE WERE NO INJURIES OF ANY KIND AND AFTER A POSTFLT INSPECTION OF THE ACFT THE ONLY DAMAGE FOUND WAS A DEFLATED L OUTBOARD MAIN GEAR TIRE WHICH ALSO CAME OFF ITS RIM. ALL CHKLISTS WERE COMPLETED AND THE ACFT WAS SECURED. WE COORDINATED WITH FLT CTL; OPS; LCL ARPT AUTHS; FAA; UNION; ETC TO ENSURE PROPER HANDLING OF THE ACFT; PAX; BAGGAGE; AND REQUIRED RPTS/PAPERWORK. AFTER MUCH THOUGHT AND REFLECTION ON WHAT HAPPENED; THE CAPT AND I BOTH BELIEVE THAT THE COMBINATION OF 2 FACTORS LED TO THIS INCIDENT: 1) THE JAMMING OF THE PWR LEVERS AT THE FLT IDLE GATE; AND 2) THE REDUCED BRAKING ACTION ON RWY 5 DUE TO THE APCHING WINTER STORM. AS OF NOW; I DON'T KNOW WHY OR HAVE LEARNED OF ANY REASON WHY THE PWR LEVERS JAMMED AND AM CONSIDERING IT A FLUKE MALFUNCTION. AT FLT IDLE; THIS ACFT WAS PRODUCING ABOUT 15-20% TORQUE RESULTING IN A HIGH SPD TAXI -- NOT WHAT YOU WANT WHEN TRYING TO TURN OFF A RWY WITH LIMITED BRAKING. ACTUALLY; BY ITSELF THAT FACTOR WOULD NOT HAVE CAUSED THE INCIDENT IF NOT FOR FACTOR #2. THOSE 2 FACTORS TOGETHER DID NOT LEAVE THE FLT CREW WITH ENOUGH STOPPING PWR TO KEEP THE PLANE ON THE PAVED SURFACE. AS FAR AS PERFORMANCE; I BELIEVE WE DID A GOOD JOB WORKING TOGETHER AND REACTING TO THE CONDITIONS WE FOUND OURSELVES IN. WE DIDN'T USE THE EMER BRAKING HANDLE BECAUSE BY THE TIME WE REALIZED WE WERE NOT GOING TO BE ABLE TO STOP ON THE RWY SURFACE; BRAKING WAS NOT EFFECTIVE AND THE CAPT WAS CONCENTRATING ON STEERING THE PLANE TO CLR APCH LIGHTS AT THE END OF THE RWY. LIKEWISE; THE THOUGHT OF SHUTTING DOWN THE ENGS CAME UP BUT WAS NOT DONE SO AS TO KEEP SOME HYD PRESSURE FOR WHAT LITTLE NOSEWHEEL STEERING THERE WAS; AGAIN THINKING OF AVOIDING LIGHTS AND FURTHER DAMAGE TO THE PLANE.