The work deals with improving the method of a complex estimation of highway maintenance quality. The methods of estimation of highway maintenance quality were analyzed. The most complete and reasonable estimation is reached using a complex method. This method takes into account the influence of different transport and operating characteristics on providing secured speed of cars. The car speed impacts on the efficiency of motor traffic. One of the indices influencing the car speed is a road

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... ness. Today, in the Russian Federation the road roughness is estimated using the International Roughness Index (IRI). But the complex method doesn't take into account the state-of-art measuring means as well as the International Roughness Index (IRI). The theoretical and experimental studies were carried out to establish the dependence between the IRI index and a partial coefficient of providing the design speed of cars. The model to define the partial coefficient of providing a design speed based on the International Roughness Index (IRI) was offered. The table for calculation of the partial coefficient of providing a design speed was offered as well.