[SystemSafety] Small but useful Detail on Road Stopping Distances

[Les Chambers]

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] ...

Les
[1] F. Scott Fitzgerald, The Great Gatsby
-----Original Message-----
From: systemsafety-bounces at lists.techfak.uni-bielefeld.de
[mailto:systemsafety-bounces at lists.techfak.uni-bielefeld.de] On Behalf Of
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.


Cheers,

-- steve



-----Original Message-----
From: <systemsafety-bounces at lists.techfak.uni-bielefeld.de> on behalf of
David Haworth <david.haworth at elektrobit.com>
Organization: Elektrobit Automotive GmbH
Date: Wednesday, July 29, 2015 11:18 PM
To: Peter Bernard Ladkin <ladkin at rvs.uni-bielefeld.de>
Cc: 'The System Safety List' <systemsafety at techfak.uni-bielefeld.de>
Subject: Re: [SystemSafety] Small but useful Detail on Road
Stopping	Distances

Peter,

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" ;-)

* For people not familiar with the German guidelines, you take your
speed in km/h, divide by two, and that gives you your "safe" distance
in metres.

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.

Cheers,
Dave


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