b. Single-track sidings. To allow passing
of trains when they are running in opposite
directions or moving at different speeds in the same
direction on single-track lines, sidings are used.
Their turnouts may be sharp and need not be
remotely controlled, since one of the trains must
ordinarily stop before entering or leaving the siding.
PERMISSIBLE SPEEDS THROUGH
The speed requirement to be met on a
particular track determines the number of the frog
and the length of the switch rail used in a turnout.
On a military railroad, the No. 8 frog and the 16 1/2-
foot switch rail are standard. On civilian railroads,
Nos. 7, 8, and 9 frogs are used for yard movements;
Nos. 10, 11, and 12 for slow-speed main and branch
lines; and Nos. 12, 15, and 20 for high-speed main-
line movements. A rule of thumb gives maximum
permissible speed in miles per hour through a
conventional turnout as equal to twice the frog
number. In table I are
Figure 2.17. Typical Crossover.
Table I. Permissible Speeds Through Various Turnouts
*To convert miles per hour to kilometers per hour, multiply the mph figure by 1.61. Example: 45 x 1.61 = 72.45
or approximately 72 kmph.