(a) Except where approved traffic signals are used to control traffic, the state highway commissioner shall erect stop, yield or merge signs at every entrance to a state trunk line highway from intersecting highways or streets. However, after a traffic engineering investigation the state highway commission acting jointly with the commissioner of the Michigan state police may give preference to a city street or a county road over a state trunk line highway, and shall erect appropriate signs.

    (b) Where 2 or more state trunk line highways intersect or cross, the state highway commissioner and the commissioner of the Michigan state police, acting jointly, shall determine which traffic, if any, shall be given preference and appropriate stop, yield or merge signs shall be erected.