Page 332 - (DK) The Ultimate Visual Dictionary 2nd Ed.

RAIL AND ROAD

Train equipment MECHANICAL SEMAPHORE SIGNAL
Red, square-ended
arm in raised position
means “all clear”
MODERN RAILROAD TRACK consists of two parallel steel rails clipped
on to a support called a railroad tie. Railroad ties are usually made of
reinforced concrete, although wood and steel are still used. The distance
Red glass
between the inside edges of the rails is the track gauge. It evolved in Britain,
which uses a gauge of 4 ft 8½ in (1,435 mm), known as the standard gauge. As
engineering grew more sophisticated, narrower gauges were adopted because Green glass
they cost less to build. The loading gauge, which is equally important, determines
the size of the largest loaded vehicle that may pass through tunnels and under
bridges with adequate clearance. Safe train operation relies on following a Actuating
lever system
signaling system. At first, signaling was based on a simple time interval between
trains, but it now depends on maintaining a safe distance between successive
Motor operating
trains traveling in the same direction. Most modern signals are color lights, but
“home” stop
older mechanical semaphore signals are still used. On the latest high-speed lines, signal
train drivers receive control instructions by electronic means. Signaling depends
on reliable control of the train by effective braking. For fast, modern trains,
which have considerable momentum, it is essential that each vehicle
in the train can be braked by the driver or by a train control Green glass
system, such as Automatic Train Protection (ATP). Braking is
achieved by the brake shoe acting on the wheel rim (rim brakes), Yellow glass
Yellow,“distant”
by disc brakes, or, increasingly, by electrical braking.
warning arm
in horizontal Tubular
FOUR-ASPECT COLOR LIGHT SIGNAL
position means steel post
“caution”
Lifting lug
Glass Ladder
(yellow) Lamp shield
Clip
Glass
(green)

Yellow
glass (lit) Electrical
relay box
Glass
(red) Base

FRONT VIEW SIDE VIEW
HOW A MODERN MAIN-LINE SIGNALING SYSTEM WORKS
Green “all clear” light
instructs train B to proceed
Red “stop” light instructs Green “all clear” light into this section of track
next train not to enter instructs train B to proceed
this section of track into this section of track Green “all clear” light
instructs train B to proceed
into this section of track
Pantograph Catenary

Train B Track

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