Except to the extent preempted by federal law, the right to fix and regulate the speed of railway trains within the limits of any city or town other than a first-class city, and at grade crossings as defined in RCW 81.53.010 where such grade crossings are outside the limits of cities and towns, is vested exclusively in the commission: PROVIDED, That RCW 81.48.030 and 81.48.040 shall not apply to street railways which may be operating or hereafter operated within the limits of said cities and towns.