listed the permissible speeds at which trains may pass through turn-outs having certain frog numbers and switch-
rail lengths.
2.17.
SUMMARY
Yard turnouts are usually sharp, and manually operated switches are used because of the limited space in
yards and the low speeds required in them. Remote-control interlocking plants usually control track routing in
passenger terminals.
A crossover is used for diverting trains from one parallel track to another, passing, reaching station
platforms, and getting off the main track. A crossover requires two turnouts with a track between them, but sharp
ones are not desirable because they restrict the speed of the trains using them. If possible, the turnouts should be
the same size and use the same rail section as the tracks they join. Single-track sidings permit passing of trains
running in opposite directions or at different speeds in the same direction. Turnouts to these sidings may be sharp
and manually controlled. "Twice the frog number" is the rule of thumb applied to find the permissible speed
through a turnout. But the speed is also controlled by the length of the switch rail.
Section III. Construction
2.18.
GENERAL
Plans and data for installing a turnout must be worked out by an engineer or a skilled turnout technician,
because a knowledge of trigonometry is needed. The computations for locating the parts of a turnout can be
complicated, especially if curves are involved. However, standard plans and data tables are obtainable. In
addition, civil engineering handbooks contain exhaustive treatments of various design problems which may occur.
When briefing the track foreman and men, the track supervisor should be able to give them the when,
why, where, and how of turnout construction. His notes in answer to these questions follow in the remaining
paragraphs of this section.
2.19.
WHEN, WHY, AND WHERE
Turnouts are installed during new construction and during out-of-face renewal of track, and when existing ones
are no longer satisfactory, because of increased speed requirements or changes in locomotive design. Turnouts
may lead from one tangent track to
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