(1) General rule. Overhead clearances shall be at least twenty-two feet six inches unless one of the provisions in this section applies.

(2) Buildings.

The overhead clearance inside of entirely enclosed buildings may be reduced to eighteen feet, if the tracks terminate within the building. When an overhead clearance of less than twenty-two feet six inches is established in a building, all cars, locomotives or other equipment must stop before entering it. The conditions provided to require the stop must be approved by the commission. Engine houses and car shops are exempt from these regulations.

(3) Trains in tunnels, under overcrossings, and on bridges.

Minimum overhead clearance in tunnels, under overcrossings, and on bridges may be decreased to the extent defined by the half-circumference of a circle having a radius of eight feet and tangent to a horizontal line twenty-two feet six inches above top of rail at a point directly above the centerline of track.

(4) All other structures.

Minimum overhead clearance may be decreased to the extent defined by the half-circumference of a circle having a radius of eight feet six inches and tangent to a horizontal line twenty-two feet six inches above top of rail at a point directly over the centerline of track.

(5) Overhead clearance of wires.

All overhead wires must have a minimum vertical clearance of not less than that specified by the safety rules for the installation and maintenance of electric supply and communication lines as provided by the rules for electrical construction and the electrical and communication workers safety rules of the state of Washington.