HAVING JUST STARTED THE CAR AND ENROUTE TO MY DESTINATION, I WAS ON A CITY STREET FOLLOWING A LARGE LANDSCAPE TRUCK TRAVELING APPROXIMATELY 20-25MPH.. ROAD CONDITIONS WERE DRY. ALTHOUGH THE TRUCK'S BRAKE LIGHTS WERE NOT ON, I PERCEIVED THE TRUCK WAS GRADUALLY SLOWING. IN ANTICIPATION OF MAKING A STOP, I MOVED MY FOOT FROM THE ACCELERATOR TO THE BRAKE PEDAL. WHEN THE TRUCK'S DRIVER APPLIED HIS BRAKES, I ALSO APPLIED MY BRAKES INTENDING TO COME TO A GENTLE STOP BY LIGHTLY PRESSING THE BRAKE PEDAL. WITHOUT WARNING THE BRAKE PEDAL 'SOFTENED' AND MY PRIUS CONTINUED TO COAST WITH NO BRAKING AT ALL. SINCE THE TRUCK'S SIZE AND WIDTH OBSCURED SIGHT OF ANY ON-COMING TRAFFIC, I COULDN'T TURN OUT OF MY LANE AND AS A RESULT REAR- ENDED THE TRUCK. SINCE THERE WAS NO DAMAGE TO THE TRUCK OR INJURIES, A POLICE REPORT WAS NOT FILED; HOWEVER, I IMMEDIATELY CALLED MY INSURANCE AGENT AND WAS AUTHORIZED TO DRIVE TO AN APPROVED BODY SHOP. AFTER THE REPAIRS WERE COMPLETED, I SCHEDULED AN APPOINTMENT ON MARCH 19TH 2010 WITH MY TOYOTA DEALER TO CHECK MY CAR'S BRAKING SYSTEM. THE BRAKE PADS/SHOES, BRAKING FLUID WERE FOUND TO BE FINE, BUT NO ANALYSIS OF THE COMPUTER BRAKING SYSTEM WAS DISCUSSED. ACCORDING TO THE TOYOTA SERVICE ADVISER, THE BRAKING FAILURE COULDN'T BE DUPLICATED AND THEIR MECHANIC FOUND NOTHING MECHANICAL THAT MIGHT HAVE CAUSED THE PROBLEM. I AM DISSATISFIED WITH TOYOTA'S SERVICE ADVISER'S DISMISSIVE POSITION REGARDING MY BRAKE'S FAILURE. DESPITE THEIR INABILITY TO DIAGNOSE THE PRO