Trailing moves for the main-line side now force the points against spring tension.
Derails are used to deliberately run a car or train off the rails to prevent its colliding with another or its
going into an open, movable-span bridge. The only place they are used on a main line is at the approach to such a
bridge. To prevent cars from running away or fouling a main track, derails are installed on storage tracks,
industry or depot connections, and similar spurs, especially when such tracks descend toward the main line.
Logically, equipment derailment is preferred to a locomotive's going into a river because of an open bridge or
onto a main line when a through train is passing the junction.
Split-point and frog derails are the two designs commonly used. The split-point derail, illustrated
in figure 2.19, a simple switch mechanism that leads
the car off the track, could be described as a switch
with no frog. Only one switch point is necessary,
and the curved stock rail leads nowhere. A derail
may be operated either manually or by remote
control. The arrow in figure 2.19 points to the
switch rod connected to the manually controlled
switch-throwing mechanism. The derail frog, shown
in figure 2.20, fits over one rail. Its grooved contour
guides the wheel flange up, over, and away from the
Figure 2.19. Split-Point Derail.
Figure 2.20. Derail Frog.
be avoided, they are sometimes necessary. Such
track crossings are either cast solid or made of built-
up rail sections. Normally, built-up ones are used on