PDFWAC 480-60-090
Narrow gauge railroads transporting freight cars.
(1) Side clearances.
For the operation of equipment on narrow gauge tracks, the side clearances and distances between centerlines of tracks must provide a distance from the sides of cars, or between the widest cars operated, not less than those distances provided by these rules for cars ten feet ten inches in width operated on standard gauge tracks.
(2) All other requirements of these rules, where applicable, must be observed by narrow gauge railroads.