[Tagging] Prevoting: New_barrier_types
John F. Eldredge
john at jfeldredge.com
Fri Jul 1 02:06:46 BST 2011
aul Johnson <baloo at ursamundi.org> wrote:
> On 06/30/2011 02:50 PM, John F. Eldredge wrote:
> > Paul Johnson <baloo at ursamundi.org> wrote:
> >> On 06/30/2011 10:37 AM, M∡rtin Koppenhoefer wrote:
> >>> Folk, I rediscovered an old proposal which is extending the set of
> >>> barrier values.
> >>> Please comment now on this, before we can eventually vote to get
> >> this
> >>> to a more definite status:
> >>> Cheers,
> >>> Martin
> >> The rope barrier pictured is actually a crash fence commonly used
> as a
> >> cost saving measure on motorway medians in the US. They're not
> >> particularly effective against anything other than SUVs; cars tend
> >> go
> >> under them and hgvs tend to go through them making them more or
> >> worse than nothing.
> > The "rope" barriers along motorways in the USA tend to be
> considerably sturdier than the wood-post-and-single-rope type shown in
> the wiki photograph. The rope barrier shown in the photograph is the
> sort that might be used along a park roadway, to discourage people
> from parking on the shoulder of the roadway. The motorway type tend
> to have steel I-beam posts, about one meter high, with multiple steel
> cables, and are fairly effective at stopping automobiles. SUVs and
> heavy goods vehicles tend to topple over the barriers, due to their
> high center of gravity.
> That's odd; I've yet to see any of the cable barrier installations in
> the northwest actually stop a car...usually they pass under the cable
> the ditch below or big rigs just blow through 'em without much effect
> the speed of the truck. I've only seen SUV's get caught in 'em,
> I will concede they do tend to roll over on impact.
This may be a factor of how low off the ground the bottom row of cables are located. Here in Tennessee, solid guardrails are mostly used. Cable barriers, when used, tend to have the bottom cable about the same distance off of the ground as the bottom of a solid guardrail, and the topmost cable about the same height as the top of a solid guardrail. So, only a wedge-nosed sports car would be likely to go under the cables. Admittedly, since most of the car/guardrail crashes that I have seen involved the solid guardrails, I am working from a small data set.
John F. Eldredge -- john at jfeldredge.com
"Reserve your right to think, for even to think wrongly is better than not to think at all." -- Hypatia of Alexandria
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