Rule 38.4.406 - OVERHEAD CLEARANCE IN TUNNELS AND BRIDGES(1) Minimum overhead clearance in tunnels and through bridges may be decreased to the extent defined by the half-circumference of a circle having a radius of eight (8) feet and tangent to a horizontal line twenty-two (22) feet six (6) inches over top of rail at a point directly over the centerline of track.NEW, 1978 MAR p. 1485, Eff. 10/27/78.Sec. 69-14-116, MCA; IMP, Sec. 69-14-116, MCA;