[SystemSafety] Interesting new publication about safety for autonomous vehicles

Olwen Morgan olwen at phaedsys.com
Thu Jul 11 11:29:20 CEST 2019

And another thing ...

London Underground signalling was always safer that BR signalling 
because of the use of interlocking machines. These are units containing 
a set of vertical bars and a set of horizontal bars. Notches in the bars 
ensure that they can only fit together in a finite number of 
configurations, each of which corresponds to a safe setting of signals 
and points. It is physically impossible to set the points into a state 
such that two trains would be on a collision course with each other 
(except for a separation violation on the same track with trains heading 
in the same direction).

Gauge violations are possible as, for example, at Barons Court (and a 
few other stations) where it is technically possible for a large 
sub-surface train (as on Circle and District lines) to be routed into a 
tunnel for smaller deeper lines. Again the safety measure is simple and 
physical. At the entrance to the smaller bore tunnel there is a U-tube 
containing mercury. A big train trying to enter a small tunnel will 
break the U-tube, cause the mercury to be release and thereby break a 
circuit causing the traction current to be shut off.

The interlocking machines are prone to wear and all the switching is in 
relays which are prone to spark erosion. On the other hand, a direct 
software simulation of the interlocking states has always seemed to me 
to offer the best route to attain a fundamentally correct point-setting 



On 11/07/2019 08:50, Olwen Morgan wrote:
> On 10/07/2019 23:35, Bruce Hunter wrote:
>> Hi Eric,
> <snip>
> Autonomous vehicle safety does seem to miss the rigour of driverless 
> trains despite missing the advantage of being confine to tracks.
> <snip>
> AFAI can see, being confined to tracks is the source of *all* the 
> safety advantages that autonomous trains have over autonomous cars. It 
> solves a problem almost entirely in physical engineering. No-one in 
> their right mind should expect software engineering to do it better 
> without tracks.
> regatrds,
> Olwen
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