The similarity between the gage of British and American railroads made possible the race
between the Baltimore and Ohio's "Royal Blue" and the London, Midland and Scottish's
"Coronation Scot, " between Washington and Jersey City in the late 1930's. Had you been
present anywhere along the line, you would have seen a surprising difference in the size of the
two trains. The "Coronation Scot" was lower and narrower than the "Royal Blue. " The
difference would have been apparent between any British train and one from the United States.
The "Coronation Scot" had to be smaller than the "Royal Blue" to pass through tunnels, between
station platforms, under bridges, and between structures along an English line. Rail equipment
must be made to conform to these clearance limitations.
A track-clearance chart or diagram is prepared for each section of a railroad, showing the
maximum dimensions of rail equipment and load that can pass over the line. The clearance chart
is of primary importance to those in the transportation department who must route odd-sized
shipments. It is also important to the maintenance official since he must be careful not to restrict
existing clearances in his maintenance work. For example, he cannot raise track in tunnels or
under bridges without authority from higher headquarters. Nor may he change alinement if such
restricting elements as structures or walls are nearby.
Illustrated in graphic form in figure 1.10 are some of the more common clearances that
are typical of those involved. The sketch is not drawn to scale nor are the dimensions necessarily
those of any specific track-clearance diagram. They are shown with an outline of a car on the
tracks to emphasize the importance of proper understanding of clearance limitations. Two track-
clearance diagrams, one for bridges and one for a single-track tunnel, designed by the American
Railway Engineering Association (AREA), are shown in figure 1.11.
An important principle of railroading and of maintenance of way is that any railway
maintenance or construction problem must be solved in relation to the density and type of traffic
the line carries or expects to carry. The path the rail line follows is called its alinement, or
ground plan--stretches of straight (tangent) track connected by arcs or curves. When looking at
the side of the rail, you see its profile, that is, its ups and downs. Steepness of grade in the
United States is expressed in percent. Standard gage in this country is