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Topic Title: Slugs and Traffic Lights
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Created On: 02 February 2011 02:30 PM
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 02 February 2011 02:30 PM
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petersheppard

Posts: 92
Joined: 18 September 2001

In a recent enquiry it appears that a slug was a causal factor in a road accident - see
http://www.telegraph.co.uk/new...ic-light-failure.html

In the railways we use "slugged" relays, but never slugged circuit boards!
All joking aside (as there was a fatality) what are the views on the transport/safety forums regarding this. It is not explicit, but it can be deduced that the failure caused the lights to go off and that was a cause in the accident.
My question is, it is normal practice in the railways to coat circuit boards with a "conformal coating" to protect against damp etc. (not come across slug trails before though!) what is the practice in the Highways area? Also, what sort of SIL (according to IEC61508) are traffic light controllers designed to.

Cheers

Peter

-------------------------
Peter Sheppard
Chair IET Transport Sector
Member Transport Policy Panel
 04 February 2011 07:41 PM
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amillar

Posts: 1918
Joined: 28 May 2002

I had a look round to try to find out if it had failed green or black - unfortunately as all the news reports seem to be copies it doesn't seem possible to tell. If it did fail to black (as is implied in some places) then I guess they could be SIL4?

As you say, it would be very interesting to know.

I have to say, with the best will in the world it is hard to defend yourself against a determined slug. Of course I agree conformal coating is a good start, but I would never quote it as a fail-safe preventative - apart from anything else it can be stripped by rat urine! (It's a lovely job analysing SIL4 failure modes ) But what should be possible is to ensure that the signal fails black.

-------------------------
Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert
 05 February 2011 10:09 PM
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alancapon

Posts: 5766
Joined: 27 December 2005

This article in the daily mail: http://www.dailymail.co.uk/new...lled-teenage-girl.html would seem to suggest that the two sets of lights failed to green.

Regards,

Alan.
 08 February 2011 10:54 AM
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petersheppard

Posts: 92
Joined: 18 September 2001

That is the only paper that says that, all other reports state that the lights failed off/dark.

Cheers

Peter

-------------------------
Peter Sheppard
Chair IET Transport Sector
Member Transport Policy Panel
 08 February 2011 12:59 PM
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amillar

Posts: 1918
Joined: 28 May 2002

I tried following up the clues in the Daily Mail report to see if the inquest report was available, sadly it didn't seem to be.

-------------------------
Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert
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