Passenger Vehicle Braking Performance with a Disabled Vacuum Power Booster

When the vacuum-powered brake booster in a passenger vehicle becomes disabled, the brake force gain of the system is reduced significantly, and the brake pedal force required to lock the tires increases beyond the ability of some adults. In such cases, the maximum braking deceleration acheived by those individuals will be something less than the upper boundary as defined by available traction.

This paper's goal is to review the design of vacuum boosters, the literature concerning human ability to depress a brake pedal, and FMVSS 105 requirements which must be met by vehicle manufacturers, and to present performance data with and without the booster operational for four passenger vehicles. Furthermore, the application of this information to accident investigations involving disabled boosters will be discussed.