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Heavy lorries and trailer combinations cause many serious traffic accidents. Improvements in inspection methods of brake systems increase traffic safety. In Finland dynamometer measurements have been used since 1960's, and its advantages are stable measuring conditions, high repetability and short inspection time. Braking force on the wheel periphery generated by the wheel brakes is measured in the roll set of the dynamometer with the help of a power measurement device connected to it. In the vehicle inspection and in the brake repair shops, the estimation of the braking ability of vehicles based on calculated definitions of the performance of the brakes and the retardations to be achieved carried out on the basis of braking forces measured with the dynamometer. The Finnish Ministry of Transport and Communications and the

Heavy lorries and trailer combinations cause many serious traffic accidents. There in Finland alone have been approximately100 killed per year by heavy duty vehicles in 1990's. Improvements in inspection methods of brake systems increase traffic safety. In Finland dynamometer measurements have been used since 1960´s, and its advantages are stable measuring conditions, high repetability and short inspection time. The Finnish Traffic Office and the Finnish Motor Vehicle Registration Centre have been interested in correlations of road retardation and dynamometer measurements and therefore established Dynamet-brake research project in 1993. This paper contains a research which aims to find out correlations of retardation prediction for lorries and trailer combinations by comparing road braking tests and dynamometer measurements, and secondly to improve the dynamometer measurement system at inspection stations.

The roller brake dynamometer (RBD) is used to measure and evaluate the braking efficiency of road vehicles in periodic technical inspections (PTI). The quality of roller brake dynamometers is very important, to ensure adequate reliability of the periodic technical inspection and to ensure the road safety of motor vehicles. It is known that dynamometer measurements involve a large number of uncertainties. The brake force measurement covers the force mechanism, sensors, data acquisition, measuring and calculation programmes, roller diameters, friction surface, and calibration of the roller brake dynamometer. At the level of the ECE-13 regulations, the quality requirements and calibration methods are not specified. The Motor Vehicle Administration in Finland is running a project to develop quality requirements and calibration methods for roller brake dynamometers. The aim is to improve the reliability and to reduce the standard deviation at inspection stations and brake workshops.