The National Highway Traffic Safety Administration has been receiving complaints from dozens of owners of the latest third generation Toyota Prius about brake failures they've experienced. The complaints are centered on the transition from regenerative to traditional braking including the possibility that extra force is required to properly slow the vehicle.
The Detroit Bureau made an analysis and said that the issues are related to the regenerative braking system, which is a core component of Toyota's hybrid technology. The regenerative braking function enables the recapture of energy while braking. This permits the hybrid to run on electric mode rather than from the gasoline engine.
In several of the complaints, the Prius would either have diminished braking power, or a surge forward with unintended acceleration. Robert Becker, a 2010 Prius owner who spoke with The Detroit Bureau, said that what he and the others are experiencing is no runaway acceleration and that it isn't related to pressing the gas pedal.
Rather, he describes it as the loss of braking power or braking momentum when the car hits a pothole, a manhole cover, or anything resembling those. He explained that this occurrence would require the driver to press down again harder on the brakes to slow or stop the car. Another Prius owner's complaint states that he has had several incidents wherein the car surges forward when in the process of braking and hitting a bump, railroad tracks or pothole.
He also experienced the same thing on slippery, icy roads, and this convinced him that he didn't let up on the brake. He explained that the car surged as he was slowly pulling up to a stop sign and braking gently. He actually came close to hitting the car in front and by pushing down very hard on the brakes, the abs activated.
The potential danger with this issue is not so much on the occupants but on the pedestrians and other motorists, especially if you consider the frequency of lacking deceleration while approaching stop lights, stop signs and on surface streets. According to an internal NHTSA memo, the concerns are centered on pedestrian safety.
The memo states that when a bump is hit, the regenerative braking (front wheels only) cuts out, and there is a short delay until the friction braking kicks in. As a result, there is a loss of braking and there is acceleration due to the sudden end of deceleration from braking. Net impact is still a loss of braking/ increase in stopping distance. In addition, the memo says that this could be fatal for pedestrians as it happens when approaching stop lights and a pothole is hit.