(1) The minimum side clearance for bridges and tunnels is eight (8) feet.
(2) For required clearance of upper section of bridges and tunnels see ARM 38.4.406.
(3) Side clearance in through bridges and tunnels 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 above top of rail directly above centerline of track.
(4) Bridges--Lower section and structures four (4) feet high or less. Through bridges supporting track affected, hand rails, water barrels and refuge platforms on bridges and trestles, water columns, oil columns, block signals, cattle guards and cattle chutes, or portions thereof, four (4) feet or less above top of rail may have clearances decreased to the extent defined by a line extending diagonally upward from a point level with the top of rail and five (5) feet distant laterally from centerline of track to a point four (4) feet above top of rail and eight (8) feet distant laterally from centerline of track: Provided that the minimum clearance for hand rails and water barrels shall be seven (7) feet six (6) inches and the minimum clearance for fences of cattle guards shall be six (6) feet nine (9) inches.
(5) Clearances authorized in (4) , except as provided for hand rails and water barrels, shall not be permitted on any new or entirely reconstructed through bridges where the work of
trainmen or yardmen requires them to be upon the decks of such bridges for the purpose of coupling or uncoupling cars in the performance of switching service on a switching lead.