Clearange

1.8.

CLEARANCE

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.

1.9.

SUMMARY

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

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