Two fiery crashes involving tractor-trailers, one of them fatal, closed northbound I-75 at separate times and places Wednesday morning, authorities said. The victim of the fatal crash under the Dunbar Road overpass in Monroe Township, reported at 9:40 a.m., remained unidentified later Wednesday pending notification of relatives, Michigan State Police from the Monroe post said. That crash involved two semis and closed I-75 in both directions for about two hours. Southbound I-75 reopened about 11:30 a.m. and a single northbound lane reopened early in the afternoon, but two other lanes remained closed until shortly before 5 p.m., for hours thereafter. Dunbar also remained closed while the bridge was inspected for fire damage. About 6 a.m., a single tractor-trailer crashed and caught fire in Erie Township about five miles north of the state line, closing the northbound lanes there for nearly five hours but causing no injuries.