system of signalling. Originally railways relied on the time interval to
ensure the safety of a succession of trains, but the defects rapidly
manifested themselves, and a space interval, or the block system, was
adopted, although it was not enforced legally on British passenger lines
until the
Regulation of Railways Act of 1889. Semaphore signals
became universally adopted on running lines and the interlocking оf points
[switches] and signals (usually accomplished mechanically by tappets) to
prevent conflicting movements being signalled was also а requirement of the
1889 Асt. Lock-and-block signalling, which ensured а safe sequence of
movements by electric checks, was introduced on the London, Chatham and
Dover Railway in 1875.
Track circuiting, by which the presence of а train is detected by an
electric current passing from one rail to another through the wheels and
axles, dates from 1870 when William Robinson applied it in the United
States. In England the Great Eastern Railway introduced power operation of
points and signals at Spitaifields goods yard in 1899, and three years
later track-circuit operation of powered signals was in operation on 30
miles (48 km) of the London and Sout Western Railway main line.
Day colour light signals, controlled automatically by the trains
through track circuits, were installed on the Liverpool Overhead Railway in
1920 and four-aspect day colour lights (red, yellow, double yellow and
green) were provided on Southern Railway routes from 1926 onwards. These
enable drivers of high-speed trains to have а warning two block sections
ahead of а possible need to stop. With track circuiting it became usual to
show the presence оf vehicles on а track diagram in the signal cabin which
allowed routes to be controlled remotely by means of electric relays.
Today, panel
operation of considerable stretches of railway is common-рlасе; at Rugby,
for instance, а signalman can control the points at а station 44 miles (71
km) away, and the signalbox at London Bridge controls movements on the
busiest 150 track-miles of British Rail. By the end of the I980s, the 1500
miles (241О km) of the Southern Region of British Rail are to be controlled
from 13 signalboxes. In modern panel installations the trains are not only
shown on the track diagram as they move from one section to another, but
the train identification number appears electronically in each section.
Соmputer-assisted train description, automatic train rеporting and, at
stations such as London Bridge, operation of platform indicators, is now
usual.
Whether points are operated manually or by an electric point motor,
they have to be prevented from moving while a train is passing over them
and facing points have to be locked, аnd рroved tо Ье lосkеd (оr 'detected'
) before thе relevant signal can permit а train movement. The blades of the
points have to be closed accurately (О.16 inch or 0.4 cm is the maximum
tolerance) so as to avert any possibility of а wheel flange splitting the
point and leading to а derailment.
Other signalling developments of recent years include completely
automatic operation of simple point layouts, such as the double crossover
at the Bank terminus of the British Rails's Waterloo and City underground
railway. On London Тransport's underground system а plastic roll operates
junctions according to the timetable by means of coded punched holes, and
on the Victoria Line trains are operated automatically once the driver has
pressed two buttons to indicate his readiness to start. Не also acts as the
guard, controlling the opening оf thе doors, closed circuit television
giving him а view along the train. The trains are controlled (for
acceleration and braking) by coded impulses transmitted through the running
rails to induction coils mounted on the front of the train. The absence of
code impulses cuts off the current and applies the brakes; driving and
speed control is covered by command spots in which а frequency of 100 Hz
corresponds to one mile per hour (1.6 km/h), and l5 kHz
shuts off the current. Brake applications are so controlled that trains
stop smoothly and with great accuracy at the desired place on platforms.
Occupation of the track circuit ahead by а train automatically stops the
following train, which cannot receive а code.
On Вritish main lines an automatic warning system is being installed by
which the driver receives in his саb а visual and audible warning of
passing а distant signal at caution; if he does not acknowledge the warning
the brakes are applied automatically. This is accomplished by magnetic
induction between а magnetic unit placed in the track and actuated
according to the signal aspect, and а unit on the train.
Train control
In England train control began in l909 on the Midland Railway,
particularly to expedite the movement оf coal trains and to see that guards
and enginemen were
relieved at the end of their shift and were not called upon to work
excessive overtime. Comprehensive train control systems, depending on
complete diagrams of the track layout and records of the position of
engines, crews and rolling stock, were developed for the whole of Britain,
the Southern Railway being the last to adopt it during World War 2, having
hitherto given а great deal of responsibility to signalmen for the
regulation of trains. Refinements оf control include advance traffic
information(ATI) in which information is passed from yard to yard by telex
giving types of wagon, wagon number, route code, particulars оf the load,
destination
station and consignee. In l972 British Rail decided to
adopt а computerized freight information and traffic control system known
as TOPS (total operations processing system) which was developed over eight
years by the Southern Pacific company in the USA.
Although а great deal of rail 1rаffiс in Britain is handled by block
trains from point of origin to destination, about onefifth of the
originating tonnage is less than a train-load. This means that wagons must
be sorted on their journey. In Britain there are about 600 terminal points
on a 12,000 mile network whitch is served by over 2500 freight trains made
up of varying assortments of 249,000 wagons and 3972 locomotives, of witch
333 are electric. This requires the speed of calculation and the
information storage and classification capacity of the modern computer,
whitch has to be linked to points dealing with or generating traffic
troughout the system.The computer input, witch is by punched cards, covers
details of loading or unloading of wagons and their movements in trains,
the composition of trains and their departures from and arrivals at yards
,and the whereabouts of locomotives. The computer output includes
information on the balanse of locomotives at depots and yards, with
particulars of when maintenanse examinations are due, the numbers of
empty and loaded wagons, with aggregate weight and brake forse, and wheder
their movement is on time, the location of empty wagons and a forecast of
those that will become available, and the numbers of trains at any
location, with collective train weigts and individual details of the
component wagons.
A closer check on what is happening troughoud the
system is thus provided, with the position of consignments in transit,
delays in movement, delays in unloading wagons by customers, and the
capasity of the system to handle future traffic among the information
readily available. The computer has a built-in self-check on wrong input
information.
Freight handling
The merry-go-round system enables coal for power
stations to be loaded into hopper wagons at a colliery
without the train being stopped, and at the power station the train is
hauled round a loop at less than 2mph (3.2 km/h), a trigger devise
automatically unloading the wagons without the train being stopped. The
arrangements also provide for automatic weighing of the loads. Other bulk
loads can be dealt with in the same way.
Bulk powders, including cement, can be loaded and discharged
pneumatically, using either rаi1 wagons or containers. Iron ore is carried
in 100 ton gross wagons (72 tons of payload) whose coupling gear is
designed to swivel, so that wagons can be turned upside down for discharge
without uncoupling from their train. Special vans take palletized loads of
miscellaneous merchandise or such products as fertilizer, the van doors
being designed so that all parts of the interior can be reached by а fork-
lift truck.
British railway companies began building their stocks of containers in
1927, and by 1950 they had the largest stock of large containers in Western
Europe. In 1962 British Rail decided to use International Standards
Organisation sizes, 8 ft (2,4 m) wide by 8 ft high and 1О, 20, 30 and 40 ft
(3.1, 6.1, 9.2 and 12.2 m) long. The 'Freightliner' service of container
trains uses 62.5 ft (19.1 m) flat wagons with air-operated disc brakes in
sets оf five and was inaugurated in 1965. At depots
'Drott' pneumatic-tyred cranes were at first provided but rail-mounted
Goliath cranes are now provided.
Cars are handled by double-tier wagons. The British car industry is а
big user of 'сomраnу' trains, which are operated for а single customer.
Both Ford and Chrysler use them to exchange parts between specialist
factories аnd the railway thus becomes an extension of factory transport.
Company trains frequent1у consist of wagons owned by the trader; there are
about 20,000 on British railways, the oil industry, for example, providing
most оf the tanks it needs to carry 21 million tons of petroleum products
by rail each year despite
competition from pipelines.
Gravel dredged from the shallow seas is another developing source of
rail traffic. It is moved in 76 ton lots by 100 ton gross hopper wagons and
