Ah nice insight into the signal system... Shall share some
foreign information on this system.
If I recall correctly, the system is called the absolute block
system, there were once such systems in Japan (where most of my
train reseach is based on, in fact over 90 percent), used in
crossings and stations alike. For a sparse traffic like KTM in
Singapore, this system has no problem in maintaining safety; unless
there is a guy sleeping at the work and dispatched two trains in
opposing directions!
In Japan's case, it was a different thing. Train traffic was
high and such systems cannot cope with it. The token system (also
under the absolute block system) was used until the 50s-60s, when
the ATS (Automatic Train Stop) system took over. There were still
non-nationalized (in the past was Japan National Railways, now
Japan Railways and privatized) railways in the country using the
absolute block system. One example that lasted till now and went
through a serious accident was the Shigaraki Highland Railways
(信楽高原鐵道) in the Kansai Region (near Kyoto).
On 14th May 1991, an accident related to the absolute block
signal system and crew error occurred on the line. JR had earlier
started operations into the private line in lieu of the high
passenger load the previous month. There were 18 round train trips
per day in both directions on normal days, increased from original
of 16, after a new signal station with a side track has been set up
between the first two stations which covers the longest distance,
and a modified Special Absolute Block Signal system was used. JR
West added to the trips by putting additional 6 round trips to help
out due to a pottery fair at the region. It was a recipe for
disaster; a single track system, new staff at a recently privatized
JNR line, and JR West staff who are not sure of the line
structure.
On the first few days of service (April 1990), the staff did not
notice anything wrong. They dispatched trains as much as the system
could handle, making trains pass by each other at stations and the
new signal station. There were near misses, especially at the new
signal station where JR West trains would wait for the Shigaraki
Railways train to pass by.
On 14th May itself, the JR West train was dispatched from the
main line into Shigaraki Highland Railways, with a 4 car Shigaraki
Railways train (SKR-200 lightweight diesel local type train)
running on the opposite direction from Shigaraki towards the main
line. The two trains were supposed to pass by at the signal
station.
In the process, the SKR-200 4 car train was delayed, as the
Shigaraki Highland Railways staff could not solve the problem with
the special absolute block system signals that were supposed to
tell the JR West train to stop at the signal station, and give the
SKR train a green signal. They were recieving a red signal
instead.
What they not know is that the system has put priority for the
JR West train to proceed to the second station of the line before
the SKR train can be dispatched towards the first station.
It did not utilise the signal station for that train
trip.
Under frustration and possible serious delay, the SKR
train was dispatched from the second station towards the main
line/first station with a red signal. The JR West train
was also somehow dispatched (staff error on the main line side),
after the staff on both sides have resorted to let the
signal system solve the problem of stopping the trains.
This was an obvious human error case and nothing was made to stop
either party; the JR West side thought that the Shigaraki Railways
side have solved the signal problem, and the SKR side thought that
the signal system would stop the JR West train anyways.
The JR West train passed by the signal station, its crew
surprised to see no SKR train in the side track and that the signal
to the next station is green. Due to delay on the side of the JR
West train (it was waiting on the main line to let the SKR staff to
clear the problem), the train crew increased speed (estimate was
about 80 km/h, maximum for the small line) towards the next
station.
At a large wooded area with a gradual bend, the two trains
collided head-on, the JR West train at about 80 km/h and SKR train
about 60 km/h, combined collision speed of 140 km/h. The SKR train
was immediately crushed, the second carriage bending upwards with
the sheer force. The JR West train had its front crushed as well,
but due to a stronger construction, survived rather intact. 42
persons were killed, 30 on the JR West train due to its slight
overload, and 12 on the SKR train, including 5 SKR staff. 614
persons were injured in this worst train accident on a private line
involving JR and private trains.
The lesson learnt from the Japan train industry was that
lightweight trains are often made without a solid chassis; engine
and bodywork are all that maintain the train in shape. Regulations
were revised to include the safety standards of these lightweight
train models, however, the 2005 Amagaseki train accident taught us
that crash protection are still not sufficient. As a gauge, the JR
West (former JNR) Kiha 58 weighed 35-38 tons per carriage, for the
engine equipped version (Kiha 28 for non-engine/trailer), the
SKR-200 only weighed 25.7 tons.
The signal system was one big lesson as well; never to rely on a
automatic system as it is not failsafe. What exactly went through
the minds of those operating the system that day was not known, but
one thing can be sure, it took a serious accident to prove that any
type of signal system are also vunerable to errors that may lead to
large damage bills and loss of life.
The Shigaraki Highland Railways is still in operation now, using
the same system as the the day of the accident, but the automatic
component have since been removed from it. Trains now have to use
the traditional absolute block system and phone confirmation from
the next station to proceed. The signal station was also
disused.