The effect of operation of mixed traffic, that is specialized passenger transportation trains and conventional freight trains, on high-speed lines on the cost of maintaining the tracks of these lines is considered. In parallel, certain recommendations with regard to the characteristics (gradient and length) that the inclines of these lines should have so that the speeds of the freight trains are not significantly reduced are made. This phenomenon could have a negative effect on the capacity of the line and on its deterioration because of excess superelevation and the geometry of the track.