Adding switch rails to a movable-point frog crossing results in a double slip switch, shown in figure 2.23.
A train entering it on either track can be diverted to either of the tracks at the opposite end. Slip switches provide
flexibility of train movements and take up much less space than the combination of simple turnouts that would be
required to obtain the same result. They have the disadvantage of difficult and expensive maintenance. Their use
is also discouraged because their parts must be individually designed and built to fit a particular location. They
are most often seen in passenger terminals and old yards where space does not permit additional turnouts to meet
modern requirements. Slip switches are not to be built nor rehabilitated in a theater of operations. These
switches are popularly known as "puzzle" switches, probably because it is extremely difficult to look at them and
determine immediately for which route of travel they are set.
Figure 2.23. Double Slip Switch.
2.35. GANTLET TRACKS
Gantlet tracks have two frogs but no switch rails, as illustrated in figure 2.24. They are used to converge
double-track lines into less space for short distances. A typical use might be to run a double-track line over a
bridge too narrow for two tracks. The same thing could be done with two turnouts, but the gantlet track
arrangement does not require switch points nor is setting the turnout necessary. However, signal protection is
required since trains running in opposing directions cannot pass each other on the gantlet track.
Track bumpers are installed at the end of dead-end tracks to prevent equipment from being derailed and
to protect surrounding structures, etc. Typical locations are industrial spurs, blind sidings,