NORMAL TRAFFIC, DRY PAVEMENT, LEVEL SURFACE, CLEAR VISIBILITY 40 MPH. I WAS FOLLOWING IN TRAFFIC, NOT PARTICULARLY CLOSE BEHIND A FULL SIZE PICKUP TRUCK. THE TRUCK STOPPED VERY QUICKLY. I PERFORMED A 'PANIC' STOP BY DEPRESSING THE BRAKE PEDAL AS HARD AS POSSIBLE AND MAINTAINED THE PRESSURE. MY PRIUS SLOWED BUT DID NOT STOP PRIOR TO HITTING THE TRUCK. NO AIRBAGS DEPLOYED. AS I PUSHED THE BRAKE PEDAL AS HARD AS POSSIBLE, THERE WAS NEVER ANY 'CHATTERING' CHARACTERISTIC OF HYDRAULIC BRAKES BEING APPLIED WITH ACCOMPANIED ABS PULSATING ACTIVITY. I BELIEVE THERE WAS NEVER ANY 'SWITCH' BETWEEN THE HYBRID REGERNERATIVE BRAKING AND TO THE HYDRAULIC BRAKING. I TRULY BELIEVE IN ANY OTHER CAR W/O THE REGENERATIVE/HYDRAULIC BAKE SWITCH, THE CAR WOULD HAVE STOPPED IN A MUCH SHORTER DISTANCE. THE CAR IS NOW BEING REPAIRED, AFTER WHICH I WILL HAVE THE BRAKES EXAMINED. *TR