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Efforts to develope a harmonized brake standard have led to the developement and evaluation of procedures for measuring the brake balance and braking efficiency of passenger cars. The European braking regulations include a procedure for direct measurment of the braking efficiency of a vehicle equiped with an antilock system (ECE Regulation No. 13. Annex 13/EEC Directive 71/320 Annex X). The procedure is a two step process including the measurement of the peak coefficient of friction (mu) for the vehicle tire on the test surface, and then finding the maximum deceleration of the vehicle on the test surface for calculation of the braking efficiency. Tests were conducted to evaluate the feasibility of using this procedure for vehicles not equiped with ABS. Comparisons were made between the peak coefficient of friction as measured by the Annex 13 procedure and as measured by a traction trailer with the vehicle tires installed.

A number of methods and types of equipment have been developed to measure a heavy vehicle's braking forces both for use as an inspection tool and for diagnosis of brake system problems. The systems and procedures evaluated included a vehicle deceleration test, a road transducer plate, roller dynamometers, a flat plate tester, a breakaway torque tester, and an infrared brake temperature measurement system. Evaluations of these devices have been conducted to ensure that the results produced are meaningful. In general, the devices compare very well and, in most cases, were found to be useful in determining the status of a brake system.

This paper serves as the seventh report in a series of reports on NHTSA's Heavy Vehicle Brake Research Program and deals with the subject of tractor and trailer brake system compatibility. It provides a detailed definition of compatibility, discusses the factors that influence it and presents data and analyses which indicate the degree of compatibility in the heavy duty combination vehicle fleet at large. The paper suggests ways in which compatibility can be improved so that combination vehicle brake systems will be more durable and provide an enhanced level of safety.