OT: Traffic Light Control (was Re: First real-world SCADA attack in US)

Wed Nov 23 23:38:56 UTC 2011

---- Original Message -----
> From: "Jay Hennigan" <jay at west.net>

> A somewhat inexperienced technician arrived on scene rebooted the
> controller and it went back to factory defaults which are N/S vs. E/W.
> Had the conflict monitor (a circuit board with a diode array, hardware -
> not software) been correctly programmed for that intersection, it
> would have kicked back to flash. No problem.
> 
> But it wasn't.
> 
> And because the left turn arrows were hard-wired in the signal heads
> to the same wire as the solid green phase, there was a conflict.

Oops.

> Fortunately the technician heard the blaring horns and witnessed a
> couple of near-misses before an accident occurred. He put the
> intersection back on flash, dug out the print for the conflict monitor
> and programming, called for help, and got it fixed.

IME, the near miss count is enough higher than the accident count (that
I see; about 10:1 or more) to actually give me some faith in drivers.  ;-)

> Normally sane defaults in a non-standard configuration, sloppy
> procedures, and human error coupled with a failure.

Yes: but as Don Norman would ask: *where was the failure here*?  You can't
blame all of it on the field tech, even though he had the Last Clear Chance
to avoid it, if the rest of the system wasn't designed to help protect him
(procedures, labeling, packaging, etc...). 

> From a practical standpoint it is difficult for one person to observe
> more than one or possibly two phases, especially from the location of
> the controller which is typically placed a few feet away from the
> corner so that it gets run over less frequently.

This is actually easier these days, since they've started hanging a "red 
light on" bulb of about 25 watts *under* one fixture in each direction. 

> >> As such, I'd say that the probability of a conflicting green occurring
> >> and causing an injury accident is pretty low even with (relatively)
> >> modern digital signal controllers.
> >
> > Yup, it does appear that's true.
> 
> But it happens.

I sort've thought it might.

I don't suppose that made the news, since there wasn't an actual collision?

Cheers,
-- jra
-- 
Jay R. Ashworth                  Baylink                       jra at baylink.com
Designer                     The Things I Think                       RFC 2100
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