On Sun, 18 May 2008 18:20:14 +0100 someone who may be "Adam Lea"
<asrl07@yahoo.co.uk> wrote this:-
>> Variable speed limiters, automatic steering, dead man's handle, and a
>> driver's vigilance device to stop the vehicle if the driver is
>> incapacitated; just like a train.
>
>Any one of which could malfunction, unless 100% reliability is achievable
>which I doubt.
100% reliability is not achievable. However, if the systems are
designed to fail safe, which vital railway systems are, then one can
get as close to 100% safety in that particular aspect as makes
little difference. For instance, due to the design of railway brakes
failure of these systems is as close to zero as makes no difference
[1].
There is also the question of only doing enough. For example railway
speed limits are only enforced automatically in certain
circumstances, for example where the speed limit is reduced by a
large amount [2]. If there is a small reduction in speed limit then,
because the train will still remain on the rails if the driver does
nothing, there is no automatic enforcement. However, all trains are
now fitted with data recorders which record, amongst many other
things, speed and location. These data recorders are regularly
downloaded by inspectors and checked for obedience to speed limits
and other things. Those drivers considered at risk have their data
recorders downloaded more often. Drivers can also encounter a
lineside speed check anywhere, they use similar devices to those
used on the roads and there are no warning signs to warn
drivers,though like all lineside staff those checking speeds will be
wearing orange clothing. There are also numerous places where the
speed of every train is recorded by the signalbox.
On the roads steering is a possible problem. However, provided the
systems work together the problem disappears. For example if the
driver fails to react to a vigilance alert the system must not just
apply the brakes, it must also steer the car around any bend until
it stops. Should be easy enough to arrange.
[1] I can think of one brake failure in the past decade, two in the
1980s and two in the 1970s.
[2]in general. There are lines where the train speed limit is
constantly compared to the line limit and the brakes applied if the
line limit is exceeded.
--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54