A417 Missing Link campaign!

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Chris5156
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Re: A417 Missing Link campaign!

Post by Chris5156 »

jackal wrote: Tue Oct 13, 2020 08:57 There's also an image showing the existing A417 repurposed as an S2+1 A436, resulting in a 9 lane cross-section at the Gloucestershire Way green bridge.


A417 Gloucestershire Way - Copy.JPG
Possibly just a bit of misguided artistry, but that picture seems to show the two uphill lanes of the existing road being used as a two-way road, with the single downhill lane not used at all. I wonder if the idea is to make that S2 plus cycle track?
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Re: A417 Missing Link campaign!

Post by jackal »

Actually I think I'm mistaken and that's a new A436 alignment. In any case, it's definitely S2+1, as shown in the detailed plans I posted on the previous page. The artist's impression seems to depict a scene from the Fast and the Furious with cars on the wrong side of the road.
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Re: A417 Missing Link campaign!

Post by roadtester »

Eight per cent is still pretty steep for a modern HQDC.

Does anyone know what Rhuallt Hill on the A55 is?

Of course the A417/A419 corridor is no stranger to steep DCs in the form of the now bypassed section at Blunsdon, although the new bit has flattened the climb a bit.

In terms of escape lanes, I think this isn't just a question of the gradient in and off itself but the fact that it is sustained over quite a long distance, giving far more opportunity for any vehicle in trouble to run out of control.
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Re: A417 Missing Link campaign!

Post by Bryn666 »

jackal wrote: Tue Oct 13, 2020 09:29 Actually I think I'm mistaken and that's a new A436 alignment. In any case, it's definitely S2+1, as shown in the detailed plans I posted on the previous page. The artist's impression seems to depict a scene from the Fast and the Furious with cars on the wrong side of the road.
Happens all the time with artist visualisations, they also like to present 12ft tall pedestrians into the street scene for urban ones as well for some reason. Copy and paste in photoshop clearly...
roadtester wrote: Tue Oct 13, 2020 09:34 Eight per cent is still pretty steep for a modern HQDC.

Does anyone know what Rhuallt Hill on the A55 is?

Of course the A417/A419 corridor is no stranger to steep DCs in the form of the now bypassed section at Blunsdon, although the new bit has flattened the climb a bit.

In terms of escape lanes, I think this isn't just a question of the gradient in and off itself but the fact that it is sustained over quite a long distance, giving far more opportunity for any vehicle in trouble to run out of control.
There aren't any percentage signs at Rhuallt, nor escape lanes downhill, but it is definitely pushing the maximum of permissible design standards. I think it would be absolutely insane to propose an 8% gradient on a new strategic A road and not have an escape lane somewhere along the hill, but what do I know, this is the magic world of HE where vehicles behave exactly as a computer says and never fail.

For reference - the A8 in Germany, in particular the dangerous and deemed obsolete and replaced bit at Aichelberg in the late 80s, was 7%.
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Re: A417 Missing Link campaign!

Post by fras »

jackal wrote: Tue Oct 13, 2020 09:19 They are proposing 8%. The current gradient is 10%.
Indeed, yes, the drawing shows reduction from 10% to 8%, then a cutting is proposed to reduce it even further to 7%. As I suggested, it it worth the extra money to do this ? I say "retained cutting", but, of course, if the cutting is through solid rock like the railway cutting into Liverpool Lime St station, no retaining walls are needed, so the cost is just in the cutting of it.
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Re: A417 Missing Link campaign!

Post by jackal »

I can only repeat that the proposal is for an 8% gradient. This supersedes the 2019 plan for a 7% gradient.
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Re: A417 Missing Link campaign!

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Bryn666 wrote: Tue Oct 13, 2020 10:26I think it would be absolutely insane to propose an 8% gradient on a new strategic A road and not have an escape lane somewhere along the hill, but what do I know, this is the magic world of HE where vehicles behave exactly as a computer says and never fail.

For reference - the A8 in Germany, in particular the dangerous and deemed obsolete and replaced bit at Aichelberg in the late 80s, was 7%.
Is there an element of modern vehicles having better performance than when the guidelines were written, so what was unacceptable 30 or 50 years ago is acceptable now? Like France's rollercoaster TGV lines?

Whether you agree with it or not, I wonder if that forms part of HE's thinking.
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Re: A417 Missing Link campaign!

Post by Bryn666 »

Chris5156 wrote: Tue Oct 13, 2020 13:35
Bryn666 wrote: Tue Oct 13, 2020 10:26I think it would be absolutely insane to propose an 8% gradient on a new strategic A road and not have an escape lane somewhere along the hill, but what do I know, this is the magic world of HE where vehicles behave exactly as a computer says and never fail.

For reference - the A8 in Germany, in particular the dangerous and deemed obsolete and replaced bit at Aichelberg in the late 80s, was 7%.
Is there an element of modern vehicles having better performance than when the guidelines were written, so what was unacceptable 30 or 50 years ago is acceptable now? Like France's rollercoaster TGV lines?

Whether you agree with it or not, I wonder if that forms part of HE's thinking.
Brakes are definitely better, but the same outcome in the event of failure results - a big doo-doo. And even modern HGVs don't like braking over long distances and have brake fade of momentous proportions sometimes.

I bet it hasn't even entered the equation, the computer model says it will work so it will work...
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Re: A417 Missing Link campaign!

Post by Hdeng16 »

Needs a new thread probably... but what are the most modern escape lanes?

It just doesn't seem like a thing we do anymore.
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Re: A417 Missing Link campaign!

Post by DB617 »

Increasing the gradient when we know the civil engineering will cope with 7 or 8 degrees smacks of value engineering. But this was to be expected with a scheme this ambitious in terms of budget vs the current financial climate.
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Re: A417 Missing Link campaign!

Post by jackal »

Would it really be safer to encourage runaway vehicles to steer into a gravel pit at high speed rather than naturally scrub speed on the miles of uninterrupted 120kph design speed dual carriageway ahead of them? UK escape lanes are mostly at tight turns or junctions for a reason.
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Re: A417 Missing Link campaign!

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jackal wrote: Tue Oct 13, 2020 15:02 Would it really be safer to encourage runaway vehicles to steer into a gravel pit at high speed rather than naturally scrub speed on the miles of uninterrupted 120kph design speed dual carriageway ahead of them? UK escape lanes are mostly at tight turns or junctions for a reason.
It's only uninterrupted until something blocks the road ahead, like traffic on the A46 or M5 or on the approach to Gloucester.
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Re: A417 Missing Link campaign!

Post by jackal »

Presumably they could stop before they reach the A46. The road beyond that is plan B...
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Re: A417 Missing Link campaign!

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jackal wrote: Tue Oct 13, 2020 15:49 Presumably they could stop before they reach the A46. The road beyond that is plan B...
I was thinking more of a serious tailback than actually getting to the junction. The point is you can't assume it's safe for a vehicle to 'naturally brake' (go down through the gears) with their speed largely out of control on a road. Anything could happen.
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Re: A417 Missing Link campaign!

Post by SouthWest Philip »

DB617 wrote: Tue Oct 13, 2020 19:19
jackal wrote: Tue Oct 13, 2020 15:49 Presumably they could stop before they reach the A46. The road beyond that is plan B...
I was thinking more of a serious tailback than actually getting to the junction. The point is you can't assume it's safe for a vehicle to 'naturally brake' (go down through the gears) with their speed largely out of control on a road. Anything could happen.
Aim for the crash barrier and scrape along that?
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Re: A417 Missing Link campaign!

Post by ABB125 »

SouthWest Philip wrote: Tue Oct 13, 2020 21:17
DB617 wrote: Tue Oct 13, 2020 19:19
jackal wrote: Tue Oct 13, 2020 15:49 Presumably they could stop before they reach the A46. The road beyond that is plan B...
I was thinking more of a serious tailback than actually getting to the junction. The point is you can't assume it's safe for a vehicle to 'naturally brake' (go down through the gears) with their speed largely out of control on a road. Anything could happen.
Aim for the crash barrier and scrape along that?
But...but...but... that might scratch the paintwork!!!!
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Re: A417 Missing Link campaign!

Post by Big L »

ABB125 wrote: Tue Oct 13, 2020 21:33
SouthWest Philip wrote: Tue Oct 13, 2020 21:17 Aim for the crash barrier and scrape along that?
But...but...but... that might scratch the paintwork!!!!
You're right. Best to smash into a queue of traffic. Scratch loads of paintwork
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Re: A417 Missing Link campaign!

Post by DB617 »

Ah yes, Armco, known for being an excellent HGV retention device. :o
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Re: A417 Missing Link campaign!

Post by jervi »

Surly chuck it in reverse, that will slow it down right?
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Re: A417 Missing Link campaign!

Post by Bryn666 »

jackal wrote: Tue Oct 13, 2020 15:02 Would it really be safer to encourage runaway vehicles to steer into a gravel pit at high speed rather than naturally scrub speed on the miles of uninterrupted 120kph design speed dual carriageway ahead of them? UK escape lanes are mostly at tight turns or junctions for a reason.
The design of modern arrester beds has gone beyond the gravel pit, which is one of many options available.

Relying on the road itself is asking for trouble - one slow vehicle in front and that will suddenly absorb a lot of kinetic energy. You may recall in 1993 a lorry had brake fade on the 10% hill dropping down into Sowerby Bridge on the A6142. It overshot the mini-roundabout at the bottom and ended up inside a post office, having flattened a bus stop and killing 5 people as it did, the driver himself ended up as the sixth death.

The HGV was badly maintained, which was the cause of the disaster, but the road design was also thrown into the spotlight - the mini-roundabout was new, the approach had been tweaked to allow its construction and it was initially a line of enquiry.

Still, to quote HBO's Chernobyl, why worry about things that aren't going to happen?
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