This study was part of the San Francisco Cable Car Brake improvement Program conducted in the years 1986-1992.

The service (as opposed to emergency) brake in the cable cars consists of two subsystems: the wheel and track brakes.

It was concluded early in the program that the friction data that could be found in the available cources were unreliable and widely scattered. Machinery Handbook, McGraw-Hill, 1973, reads on page 542 that "[v]alues of coefficients of frictions reported by various experimenters depend on conditions surrounding tests and on test procedures. Even slight changes in these conditions and procedures often result in significant variations of coefficients."

In addition, a need has developed for an inquiry into the nature of braking, where, as in the cable cars, two systems of braking--wheel and track--have been acting at the same time. Further complications were caused by the fact that two types of track brake were investigated, mechanical and hydraulic, each with a widely different level of applied force.

In view of the circumstances described above, only after a considerable body of test data had been collected could an attempt be made to develop a broader picture of cable car braking. It is believed that these findings will, in turn, guide further testing and development of improved cable car brake hardware.

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