Inspection of pavement top layer of recently reconstructed streets in Riga has revealed distinct longitudinal deformations or rutting. Such deformations reduce traffic safety and comfort. The present research aims at determining the causes of rutlike deformations in type SMA asphalt concrete pavement and working out recommendations for their prevention. In the course of research ruts were classified according to their origin, possible causes dented and displaced ruts were advanced and the experimental part outlined: in laboratory conditions to analyze change of mechanical properties of type SMA asphalt concrete at different temperatures. It was found that unmodified bitumen used for making type SMA asphalt concrete lacks viscosity and adhesion at high temperatures. It was also concluded that these temperature exceed softening point of bitumen and in time coincide with the period of highest traffic intensity in city streets.