 The Machynlleth interlocking plant: turn-of-the-century technology still in daily use. |
"Shake
off the rain, put your things down. So
you're a railway enthusiast, eh? Would you like a coffee?" I gave my name
and allowed as how I was indeed a railfan, from the States, and would very much like a
coffee. My host busied himself setting up the waterpot on a small electric ring, and
we chatted while the water heated: I learned that this gracious man was John Gwynne, a
career railwayman first with BR and now with Railtrack, the new privatized railway
infrastructure company. Encouraged by John, I began to poke about the tower.
Larger than it looked from the platform, the tower stretched at least 30 feet
from end to end. Running the entire way down the trackside wall was a classic manual
or "armstrong" interlocking plant and a model board covering the whole station
and yard complex. On the back wall, opposite the levers, stood a desk loaded down
with three computer monitors and an intimidating array of phones, radios, keyboards, and
communications equipment. In contrast to the peeling paint on the exterior walls of
the tower, everything inside-- the interlocking levers, the desks, the very floor itself--
was polished, well tended, and spotlessly clean.
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 John Gwynne confers with a maintenance of way foreman out on the line from his controller's desk. |
After
fussing with the instant coffee and
proffering the sugar and cream, John led me on a walk-through of the tower. The manual
plant, he explained, covered far more than the Machynlleth depot alone: through relays and
signal lines, its levers actually set the turnouts and signals all the way to Dovey
Junction, four miles down the way. Yet the interlocking plant was just the beginning
of John's responsibilities. Gesturing at that deskfull of computer screens tucked
away in the back corner, he explained that they constituted a Radio Token signaling system
which covered the entire remainder of the Cambrian lines outside the Machynlleth
interlocking. No humble towerman, John was actually the first-trick controller or
dispatcher for the entire railway grid of mid-Wales.
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| Pulling
up a second chair so I might watch, John put
the radio token system through its paces for me. Each of the screens held a schematic
track diagram-- essentially a computerized model board. Together the three consoles
covered the entire line from Shrewsbury over the English border down to Machynlleth, and
from Dovey Junction on to Aberystwyth in the south and Pwllheli in the north. As
John explained it, the cab of each train on the line was equipped with brackets and a data
socket, into which the driver could plug a small portable video terminal. A radio
data link connects the terminal in each train to John's central facility. Using his
keyboards, John can set up routings on his screens, and then assign movement authority to
individual trains by transmitting a "radio token" to the driver. Once John
transmits the token, a set of repeater stations relays the signal to the train out on the
line. An onboard computer decodes the signal and displays the new movement authority
on the cab video screen, and the driver opens up the throttle and proceeds into the track
for which he now holds the "token."
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| As I
followed John's explanation, I was struck by
the way the BR and its successor Railtrack had gone back to the future in designing the
system. Saddled with an aging and expensive physical plant of lineside signals and
interlocking towers for controlling train movements on the Cambrian lines, BR knew that it
needed to cut costs: the alternative might be partial or full closure of the entire route.
In response, they decided to replace the expensive lineside signaling equipment
with a compact and up-to-date system of computers, video screens, and radio data links.
Yet conceptually, the Radio Token system represents a return to the fundamental
practices of the steam era. Though video consoles and radio signals replace the
electromechanical token machines and their metal chits, there is no functional difference
between Railtrack's Radio Token dispatching and the Victorian ways of the tiny Talyllyn Railway.
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