Re: [SystemSafety] Small but useful Detail on Road Stopping Distances

From: Les Chambers < >
Date: Fri, 31 Jul 2015 10:15:51 +1000

Then there's the issue of field of vision. If you're stopping distance exceeds your field of vision you are an accident waiting to happen. Common hazard scenarios:
1. Descending a mountain on a bicycle. You come around the corner and are faced with joggers, rocks on the road, a pothole that wasn't there last time, trees on the road, mudslides, cars on the wrong side of the road passing cyclists coming up. You can't change your line. This is almost impossible on a two wheeled vehicle at speed. So you grit your teeth and plough into whatever it is.
2. Driving into a blizzard. One minute it's clear and the next you've got a whiteout. Behind you the good-old-boys in the swamp vehicles just keep coming like nothing has happened. This happened to me once on a freeway in Michigan. By pure luck I had a vehicle behind me. The good-old-boy hit him instead.
3. Driving into an un-commanded deluge in a road tunnel. One minute all is fine, the next you can't see anything. One tunnel I worked on could deliver 6000 litres of good firefighten water per minute in a 300 metre section of tunnel. Just like the previous example of flying an ultralight into a cloud, all would be okay if no one panicked. But inevitably someone does and you get the pileup.
As safety authority I attempted to push this as a major hazard. During commissioning the system had already demonstrated it was capable of doing this. Someone took me aside and said, "Les why are you so negative." And ... so we beat on, boats against the current drawn back ceaselessly into the past[1] ...

[1] F. Scott Fitzgerald, The Great Gatsby -----Original Message-----
From: systemsafety-bounces_at_xxxxxx [mailto:systemsafety-bounces_at_xxxxxx Steve Tockey
Sent: Friday, July 31, 2015 12:38 AM
To: David Haworth; Peter Bernard Ladkin
Cc: 'The System Safety List'
Subject: Re: [SystemSafety] Small but useful Detail on Road Stopping Distances

We were taught (in the US), "One car-length per 10 MPH" as in if you're going 50 MPH then leave 5 car lengths distance between your car and the one in front.


-----Original Message-----
From: <systemsafety-bounces_at_xxxxxx David Haworth <david.haworth_at_xxxxxx Organization: Elektrobit Automotive GmbH Date: Wednesday, July 29, 2015 11:18 PM
To: Peter Bernard Ladkin <ladkin_at_xxxxxx Cc: 'The System Safety List' <systemsafety_at_xxxxxx Subject: Re: [SystemSafety] Small but useful Detail on Road Stopping Distances


On 2015-07-29 15:58:35 +0200, Peter Bernard Ladkin wrote:
> The traffic law in Germany stipulates a reaction time of 1 second.

The "halber Tacho"* rule for driving on the Autobahn approximates to a 2 second reaction time (since your safe distance behind another car doing the same speed is just your reaction time, all other things being equal). Or one second plus "engineering tolerance" ;-)

Incidentally, the UK has a 2 second guideline for the same purpose. And they used to have a snappy slogan: "Only a fool breaks the 2-second rule". One advantage of this over the "halber Tacho" rule is that it is easier to apply in practice.


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systemsafety_at_xxxxxx Received on Fri Jul 31 2015 - 02:16:17 CEST

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