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Bryn666 wrote: ↑Tue Oct 13, 2020 22:13
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?
As I said, "UK escape lanes are mostly at tight turns or junctions for a reason".
Anyway, I'm not saying they shouldn't have them on the A417, just that it does seem to me a reasonable question whether there is enough of a safety benefit in this case given the lack of hazards ahead and significant economic and environmental cost (the cutting would presumably have to be widened). Certainly I would say the case for taking the gradient back to 7% is rather more obvious.
Bryn666 wrote: ↑Tue Oct 13, 2020 22:13
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?
As I said, "UK escape lanes are mostly at tight turns or junctions for a reason".
Anyway, I'm not saying they shouldn't have them on the A417, just that it does seem to me a reasonable question whether there is enough of a safety benefit in this case given the lack of hazards ahead and significant economic and environmental cost (the cutting would presumably have to be widened). Certainly I would say the case for taking the gradient back to 7% is rather more obvious.
The ones on the A2 are badly designed anyway (but remember you're not supposed to be able to drive away from an arrester bed - if you've lost your brakes to the point you need to drive into a gravel trap you SHOULDN'T be driving away) and the truck parked there is just asking for trouble - the worst offender has to be the one in the middle of the roundabout at the Eastern Docks. It rather assumes you've made it down the hill, around the sharp curve of the Jubilee Way flyover, and there isn't a queue onto the roundabout.
The length of the gradient is usually the deciding factor - if the length of 7% is less than 1km then I'd say it possibly doesn't warrant escape lanes - but once you get towards 2km+ it should definitely be a consideration even if it means widening the cutting.
https://goo.gl/maps/9cWzmqXmMrwwCctL7 this example on the French A28 is 6% and it's STEEP. It has an escape lane as it takes a sharp left turn. Don't kid yourself that 7% on a high speed dual carriageway is barely worth registering.
Bryn Terminally cynical, unimpressed, and nearly Middle Age already. She said life was like a motorway; dull, grey, and long.
Bryn666 wrote: ↑Tue Oct 13, 2020 22:13
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?
As I said, "UK escape lanes are mostly at tight turns or junctions for a reason".
Anyway, I'm not saying they shouldn't have them on the A417, just that it does seem to me a reasonable question whether there is enough of a safety benefit in this case given the lack of hazards ahead and significant economic and environmental cost (the cutting would presumably have to be widened). Certainly I would say the case for taking the gradient back to 7% is rather more obvious.
The ones on the A2 are badly designed anyway (but remember you're not supposed to be able to drive away from an arrester bed - if you've lost your brakes to the point you need to drive into a gravel trap you SHOULDN'T be driving away)
You'd hope so. Same principles for any breakdown apply there though, get out of the vehicle and find somewhere safe on the verge or behind a suitable barrier (not sat on it).
There's a lot of heavy lifting around the phrase "vehicles are more reliable" these days, unfortunately.
Bryn Terminally cynical, unimpressed, and nearly Middle Age already. She said life was like a motorway; dull, grey, and long.
Looking at the detailed plans accompanying the environmental assessment there are a number of ANPR camera along the route would they be ameliorating concerns on the gradient by instuting a 50? mph average speed.
tomuk wrote: ↑Wed Oct 14, 2020 15:56
Looking at the detailed plans accompanying the environmental assessment there are a number of ANPR camera along the route would they be ameliorating concerns on the gradient by instuting a 50? mph average speed.
Given that Option 30 (the one being taken forward) differs from whatever the alternative option was in that it has a 70mph curve under the Hot Air Balloon rather than a 50mph curve, I wouldn't have thought so.
I think 7-8 per cent is still a lot for an HQDC. I think there's likely to be a significant issue with traffic flow but not because modern cars and trucks driven competently can't handle these gradients, up or down, which of course they can with ease. I'm thinking more of the sorts of inattentive numpties who will hit the gradient going uphill without anticipating the need to change down to maintain a decent speed, and will then balk following traffic, or less experienced/disciplined drivers who don't understand engine braking or using the gears to control a car on a long downward slope, and are therefore likely to end up breaking the limit, annoying better drivers.
That said, stepping back and looking at the big picture, I'm still impressed with the latest design. For many years, before this became a live scheme, as a sort of local (my parents lived on that side of Cheltenham, so I would pass the Air Balloon most weeks when visiting them), I would speculate how the two modern dualled sections of the A417 might one day somehow be linked together, and came to the (inexpert) conclusion that given the height difference between them, and their respective orientations, this would be all but impossible.
The now abandoned tunnel solution always seemed unlikely to go ahead for financial and practical reasons, so I think the engineers have done very well to produce something that looks perhaps slightly marginal in terms of gradients and radii but still seems to be eminently workable without resorting to that sort of expense. It must have involved endless honing of the design to come up with a decent result. And it's certainly a lot better than just giving up and doing nothing, which is probably the alternative!
But in true British fashion the most difficult gap is the one which gets left until last. Commonhead and Blunsdon were done a few years and they were relatively straightforward in comparison.
Actually the Air Balloon isn't the last gap. The section west of Brockworth between the M5 and A40 is also unfinished. The tiny roundabout immediately west of M5 J11a was a temporary measure awaiting the building of the final GSJ at the Corinium Avenue junction.
How would you like your grade separations, Sir? Big and complex.
Truvelo wrote: ↑Wed Oct 14, 2020 17:39
But in true British fashion the most difficult gap is the one which gets left until last. Commonhead and Blunsdon were done a few years and they were relatively straightforward in comparison.
Actually the Air Balloon isn't the last gap. The section west of Brockworth between the M5 and A40 is also unfinished. The tiny roundabout immediately west of M5 J11a was a temporary measure awaiting the building of the final GSJ at the Corinium Avenue junction.
The Air Balloon is the last gap between the two motorways, which is where most of the traffic will be heading.
Re the gradient, the A38 and the A380 on Haldon Hill south of Exeter are both at least as steep as the proposed road and the hill is getting on for as high. There is an escape lane on the A380 but nothing on the A38. They are steep but don't cause any real issues in my experience.
Truvelo wrote: ↑Wed Oct 14, 2020 17:39
But in true British fashion the most difficult gap is the one which gets left until last. Commonhead and Blunsdon were done a few years and they were relatively straightforward in comparison
The A3 at Hindhead is another example... the tunnel is a great solution!
Just to say that there was an announcement by HE in the Daily Telegraph yesterday about the scheme, and it seeking a DCO. The consultation was also included in the announcement.
jervi wrote: ↑Tue Oct 13, 2020 22:12Surly chuck it in reverse, that will slow it down right?
If you do that you're relying on the gearbox to hold back the weight of the vehicle and all its momentum. With a 44 ton HGV, I expect the only result of putting it in reverse would be that your runaway lorry would have stripped its gears.
jervi wrote: ↑Tue Oct 13, 2020 22:12Surly chuck it in reverse, that will slow it down right?
If you do that you're relying on the gearbox to hold back the weight of the vehicle and all its momentum. With a 44 ton HGV, I expect the only result of putting it in reverse would be that your runaway lorry would have stripped its gears.
I'm neither a mechanic nor an expert driver, but I'd imagine that putting pretty much any vehicle into reverse while it is travelling forwards at speed is going to result in shrapnel being fired everywhere, a huge amount of smoke, and possibly fire... and that's if you can even find the gear while it's moving forwards, and get it to engage.
Engaging reverse in a manual geared car whilst stationary without holding the clutch down for a couple of seconds is enough to hear the sound of gears stripping.
How would you like your grade separations, Sir? Big and complex.
Decades ago my late uncle told me about a practice among some drivers of putting a car into reverse (obviously with the clutch pedal depressed!) on the motorway in order to produce a brief flash of the reversing lights. I think the object was to use this to signal a "thank you" to a following motorist - e.g. for making space to pull into after an overtaking manoeuvre.
Truvelo wrote: ↑Wed Oct 14, 2020 17:39Actually the Air Balloon isn't the last gap. The section west of Brockworth between the M5 and A40 is also unfinished. The tiny roundabout immediately west of M5 J11a was a temporary measure awaiting the building of the final GSJ at the Corinium Avenue junction.
That roundabout is rather inelegant. Always stuck me as odd that the original bypass round Hucclecote, to the east of this roundabout, was retained when Brockworth was bypassed.
There's no point in the movements between the southern arm and A417 east as they're much more direct via the big roundabout at J11a. A417 to Hucclecote can be done the same way. So instead of the roundabout it should just be a westbound merge, with the southbound carriageway no more than a farm access.
jackal wrote: ↑Sat Oct 17, 2020 21:42
There's no point in the movements between the southern arm and A417 east as they're much more direct via the big roundabout at J11a. A417 to Hucclecote can be done the same way. So instead of the roundabout it should just be a westbound merge, with the southbound carriageway no more than a farm access.
Without knowing the full eventual plan, the trajectory of the A417 travelling west when it hits that roundabout suggests to me that it would have been removed altogether, and the A417 extended onwards like this:
...though of course you could equally contrive a GSJ that would carry the mainline north instead of west.
None of that negates the fact that the roundabout doesn't have to be there at all.