[SystemSafety] Interesting new publication about safety for autonomous vehicles

Olwen Morgan olwen at phaedsys.com
Thu Jul 11 14:10:33 CEST 2019

On 11/07/2019 12:41, Peter Bernard Ladkin wrote:
> <snip>
> But rail control is further along. There are fixed blocks, and then there are moving blocks.
> Moving-block systems are in place for some low-speed lines (Victoria, Jubilee in London, I
> understand, as well as the DLR). For normal-speed intercity rail, it is part of ERTMS Level 3. I
> don't think there is a Level 3 installation yet. There are quite a few Level 2 stretches in Europe.


 >>>It is actually only a small conceptual step from fixed-block to 
moving block. In fixed block, no two trains are ever on the same track 
block at any one time. In moving block, one simply keeps track (no pun 
intended) of train positions and ensures that there is always a 
separation block of safe size between them. The basic state machine is 
more complex but can retain a structure similar to that of fixed block 
systems and is relatively simple by infrastructure engineering 
standards. The safety design effort has to be focussed on sensor and 
data transmission dependability


The two safety mechanisms road has going for it that are not available 
for rail-guided transportation is trajectory modification and very rapid 
braking. I have no idea if or how traj-mod is used in the semi-automatic 
"driver assistance" systems available nowadays. (Relatively) rapid 
braking is of course used.

 >>>You'll have gathered from my recent experience with the Mitsubishi 
Eclipse Cross that so far I've not been impressed by even the most 
modest forms of driver assistance. That PoS did not have traj-mod but 
attempted to make up for that by rapid and startling braking in 
situations where it was not necessary and a human driver would not have 
done it. If traj-mod itself behaved like that, it could quite easily 
cause injuries to people inside a car.

I'm not entirely convinced that traj-mod and rapid braking are all on 
the plus-side when comparing cars and trains.


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