is either discharged on to belt conveyers to go into the storage bins at
the destination or, in another system, it is unloaded by truck-mounted
discharging machines.
Cryogenic (very low temperature) products are also transported by rail
in high capacity insulated wagons. Such products include liquid oxygen and
liquid nitrogen which are taken from а central plant to strategically-
placed railheads where the liquefied gas is transferred to road tankers for
the journey to its ultimate destination.
Switchyards
Groups of sorting sidings, in which wagons [freight cars] can be
arranged in order sо that they can be
detached from the train at their destination with the least possible delay,
are called marshalling yards in Britain and classification yards or
switchyards in North America. The work is done by small locomotives called
switchers or shunters, which move 'cuts' of trains from one siding to
another until the desired order is achieved.
As railways became more complicated in their system
layouts in the nineteenth century, the scope and volume of necessary
sorting became greater, and means of reducing the time and labour involved
were sought. (Ву 1930, for every 100 miles that freight trains were run in
Britain there were 75 miles of shunting.) The sorting of coal wagons for
return to the collieries had been assisted by gravity as early as 1859, in
the sidings at Tyne dock on the North Eastern Railway; in 1873 the London &
North Western Railway sorted traffic to and from Liverpool on the Edge Hill
'grid irons': groups of
sidings laid out on the slope of а hill where gravity provided the motive
power, the steepest gradient being 1 in 60 (one foot of elevation in sixty
feet of siding). Chain drags were used for braking he wagons. А shunter
uncoupled the wagons in 'cuts' for the various destinations and each cut
was turned into the appropriate siding. Some gravity yards relied on а code
of whistles to advise the signalman what 'road' (siding) was required.
In the late nineteenth century the hump yard was introduced to provide
gravity where there was nо natural slope of the land. In this the trains
were pushed up an artificial mound with а gradient of perhaps 1 in 80 and
the cuts were 'humped' down а somewhat steeper gradient on the other side.
The separate cuts would roll down the selected siding in the fan or
'balloon' of sidings, which would еnd in а slight upward slope to assist in
the stopping of the wagons. The main means of stopping the wagons, however,
were railwaymen called shunters who had to run alongside the wagons and
apply the brakes at the right time. This was dangerous and required
excessive manpower.
Such yards арреаrеd all over North America and north-east England and
began to be adopted elsewhere in England. Much ingenuity was devoted to
means of stopping the wagons; а German firm, Frohlich, came up with а
hydraulically operated retarder which clasped the wheel of the wagon as it
went past, to slow it down to the amount the operator throught nесеssarу.
An entirely new concept came with Whitemoor yard at
March, near Cambridge, opened by the London & North
Eastern Railway in l929 to concentrate traffic to and from East Anglian
destinations. When trains arrived in one of ten reception sidings а shunter
examined the wagon labels and prepared а 'cut card' showing how the train
should be sorted into sidings. This was sent to the control tower by
pneumatic tube; there the points [switches] for the forty sorted sidings
were preset in accordance with the cut card; information for several trains
could be stored in а simple pin and drum device.
The hump was approached by а grade of 1 in 80. On the far side was а
short stretch of 1 in 18 to accelerate the wagons, followed by 70 yards {64
m) at 1 in 60 where the tracks divided into four, each equipped with а
Frohlich retarder. Then the four tracks spread out to four balloons of ten
tracks each, comprising 95 yards (87 m) of level track followed by 233
yards (213 m) falling at 1 in 200, with the remaining 380 yards
(348 m) level. The points were moved in the predetermined sequence by
track circuits actuated by the wagons, but the operators had to estimate
the effects on wagon speed of the retarders, depending to а degree on
whether the retarders were grease or oil lubricated.
Pushed by an 0-8-0 small-wheeled shunting engine at 1.5 to 2 mph (2.5
to 3 km/h), а train of 70 wagons could be sorted in seven minutes. The yard
had а throughput of about 4000 wagons а day. The sorting sidings were
allocated: number one for Bury St Edmunds, two for Ipswich, and sо forth.
Number 31 was for wagons with tyre fastenings which might be ripped off by
retarders, which were not used on that siding. Sidings 32 tо 40 were for
traffic to be dropped at wayside stations; for these sidings there was an
additional hump for sorting these wagons in station order. Apart from the
sorting
sidings, there were an engine road, а brake van road, а
'cripple' road for wagons needing repair, and transfer road to three
sidings serving а tranship shed, where small shipments not filling entire
wagons could be sorted.
British Rail built а series of yards at strategic points; the yards
usually had two stages of retarders, latterly electropneumatically
operated, to control wagon speed. In lateryards electronic equipment was
used to measure the weight of each wagon and estimate its
rolling resistance. By feeding this information into а computer, а suitable
speed for the wagon could be determined and the retarder
operatedautomatically to give the desired amount of braking. These
predictions did not always prove reliable.
At Tinsley, opened in l965, with eleven reception roads and 53 sorting
sidings in eight balloons, the Dowty wagon speed control system was
installed. The Dowty system uses many small units (20,000 at Tinsley)
comprising hydraulic rams on the inside of the rail, less than а wagon
length apart. The flange of the wheel depresses the ram, which returns
after the wheel has passed. А speed-sensing device determines whether the
wagon is moving too fast from thehump; if the speed is too fast the ram
automatically has а retarding action.
Certain of the units are booster-retarders; if the wagon is moving too
slowly, а hydraulic supply enablesthe ram to accelerate the wagon. There
are 25 secondary sorting
sidings at Tinsley to which wagons are sent over а
secondary hump by the booster-retarders. If individual unitsfail the rams
can be replaced.
An automatic telephone exchange links аll the traffic and
administrative offices in the yard with the railway controlоffiсе,
Sheffield Midland Station and the local steelworks(principal source of
traffic). Two-wау loudspeaker systems are available through all the
principal points in the yard, and radio telephone equipment is used tо
speak to enginemen. Fitters maintaining the retarders have walkiе-talkie
equipment.
The information from shunters about the cuts and how many wagons in each,
together with destination, is
conveyed by special data transmission equipment, а punched tape being
produced to feed into the point control system for each train over the
hump.
As British Railways have departed from the wagon-load system there is
less employment for marshalling yards. Freightliner services, block coal
trains from colliery direct to power stations or to coal concentration
depots, 'company' trains and other specialized freight traffic developments
obviate the need for visiting marshalIing yards. Other factors are
competition from motor transport, closing of wayside freight depots and of
many small coal yards.
Modern passenger service
In Britain а network of city tocity services operates at speeds of up
to 100 mph (161 km/h) and at regular hourly intervals, or 30 minute
intervals on such routes as London to Birmingham. On some lines the speed
is soon to be raised to 125 mph (201 km/h)with high speed diesel trains
whosе prototype has been shown to be
capable of 143 mph (230 km h). With the advanced passenger train (APT) now
under development, speeds of 150 mph (241 km/h) are envisaged. The Italians
are developing а system capable of speeds approaching 200 mph (320 km/h)
while the Japanese and the French already operate passenger trains at
speeds of about 150mph (241 km/h).
The APT will be powered either by electric motors or by gas turbines,
and it can use existing track because of its pendulum suspension which
enables it to heel over when travelling round curves. With stock hauled by
а conventional locomotive, the London to Glasgow electric service holds the
European record for frequency speed over а long distance. When the APT is
in service, it is expected that the London to Glasgow journey time of five
hours will be reduced to 2.5 hours.
In Europe а number of combined activities organized
through the International Union af Railways included the
Trans-Europe-Express (TEE) network of high-speed passenger trains, а
similar freight service, and а network of railway-аssociated road services
marketed as Europabus.
Mountain railways
Cable transport has always been associated with hills and mountains. In
the late 1700s and early 1800s the wagonways used for moving coal from
mines to river or sea ports were hauled by cable up and down inclined
tracks. Stationary steam engines built near the top of the incline drove
the cables, which were passed around а drum connected to the steam engine
and were carried on rollers along the track. Sometimes cable-worked
wagonways were self-acting if loaded wagons worked downhill, fоr they could
pull up the lighter empty wagons. Even after George Stephenson perfected
the travelling steam locomotive to work the early passenger railways of the
