For example, low spots may be corrected by placing ties of greater depth under the low rails. Such work requires
considerable skill, time, and expense.
If the track approaching a ballasted-deck bridge is to be given an out-of-face raise, there is no problem
because the raise may be carried across the bridge by the bridge ballast. But when the track leading to an open-
deck bridge is given an out-of-face raise, a problem arises. The bridge track must be raised on shims, or the
bridge ties must be replaced, or a suitable runoff must be provided at either end of the bridge to connect the lower
bridge track with the higher track on either side. Runoffs are usually considered the best solution, since shimming
is to be avoided as a general practice, and changing bridge ties is expensive and laborious. Rail anchors should
not be used on track over open-floor bridges. (Rail anchors are discussed in RT 670, paragraph 3.22.) Ties are so
well anchored when this type of bridge is constructed that tie movement is practically impossible, making rail
anchors unnecessary. As a general practice, the surfacing of track over open-floor, but not ballasted-deck, bridges
is done by bridge and building forces rather than by track maintenance men.
5.5.
IN INTERLOCKING PLANTS AND SIGNAL TERRITORY
An interlocking plant is a network of remotely controlled turnouts and crossovers. It may also include
crossings and always includes the mechanism controlling the switches and the signals governing trains passing
through the installation. The plants are so constructed that conflicting movements cannot be set up by the
operator, and the necessary signal indications are given automatically when any particular route is arranged. To
carry out these functions, interlocking plants are necessarily complicated in construction and invariably involve
detailed electric circuits. Much of the wiring is buried in the roadbed throughout the interlocking plant so that
extreme care is necessary in any maintenance operation which disturbs the roadbed. Personnel of the
communications and railway signal maintenance platoon should be called upon to locate this wiring when such
jobs as ballast cleaning, ballast renewal, surfacing, or lateral drainage system maintenance are to be done within
interlocking limits.
Repairing or replacing power-operated switches is another task requiring the assistance of signal
personnel who have a direct interest in the effect these mechanisms have on signals and control machines.
Similar assistance from the signal platoon is necessary when switches and rails in Centralized Traffic Control
territory or automatic block territory are replaced or repaired.
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