<p>It has been well proven that as the friction of a road surfacing decreases, the number of crashes increases, causing road death and injuries. In this research tried to study on the effect of the friction between road surface and tires on the accidents by rebuilding asphalt overlay. That has been studied in this article by studying on the information about traffic, accidents and case study concerning a street in Tehran by execution the new asphalt overlay. In order to survey the influence of execution of the new asphalt overlay, all the information about traffic volume and accidents in the said street gathered and investigated. Furthermore the result from each part compared with other researches. Results have shown that number of accidents decreased sensibly by modifying asphalt overlay and this decrease would be more at higher speeds. Therefore the method of modifying asphalt overlay is recommended in risky points to preventing or decreasing the accidents.</p>