Two separate traffic crashes on the U.S.-131 expressway just north of the Dorr exit (No. 68) Monday morning shut down the southbound lane of the freeway for about two hours. involving semi tractor-trailers and vehicles. Police directed motorists to ramp off at the exit 68 and to get back on southbound on the other side of the overpass. Authorities said the scene was cleared for all through traffic at about 4:17 p.m.