WHILE DRIVING IN HEAVY TRAFFIC ON CITY SIDE STREET, VEHICLE IN FRONT STOPPED, I ATTEMPTED TO DO THE SAME, BUT UNSUCCESSFULLY. MY VEHICLE WAS A RENTAL AND RENTAL COMPANY REPLACED IT WITH AN IDENTICAL VEHICLE. SUBSEQUENT EXPERIMENTATION WITH SAID REPLACEMENT SHOWED WHAT I BELIEVE IS A WEAKNESS IN THE ELECTRONICALLY CONTROLLED BRAKE SYSTEM. WITH ONE APPLICATION OF THE BRAKE PEDAL A CERTAIN PERCENTAGE OF BRAKE POWER IS AVAILABLE, WITH A CLOSELY FOLLOWED SECOND APPLICATION, THE PERCENTAGE OF AVAILABLE BRAKING POWER IS INCREASED, AFTER A THIRD, EVEN MORE. THE BRAKING POWER AVAILABLE AFTER THE FIRST APPLICATION IS LOW, EVEN WITH FULL PEDAL APPLICATION. THIS CONSTITUTES A HAZARD IN THE EVENT OF A NEED FOR FULL BRAKING POWER. IT IS MOST LIKELY THAT A PERSON ENCOUNTERING A SITUATION AS I FOUND MYSELF IN WOULD DO WHAT I DID, I.E. APPLY MAXIMUM PRESSURE TO THE BRAKE PEDAL ONLY TO FIND THAT BECAUSE OF THE LOW AVAILABLE BRAKING POWER THE VEHICLE, PERSON, OR ANIMAL WOULD NOT ESCAPE DAMAGE OR INJURY.