Completed Dec. 2021: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

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Herned
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by Herned »

fras wrote: Mon Jun 28, 2021 12:52 Is there a drawing, or map of this new section of road.
Streetview has been updated very recently and shows the whole eastbound carriageway
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by WHBM »

This should be easy - what's the Design Speed of the new road.

As some of the excuses are that there are short acceleration lanes, then a 50mph Design Speed should have been in the plans from the start, not announced today. If the Design Speed is a full 70mph then we can ask why the expenditure on such an alignment if traffic is not to be allowed to run at it.

And as the bulk of any emissions are from diesel HGVs, limited to 56mph, rather than 70mph cars, and as the HGVs will run on the limiter anyway, and probably not even make that on the steep uphill, where most of the power output will happen (downhill they would be coasting), just where are the calculations for emissions reductions.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by rhyds »

Design speed has always been 50mph on the section in question, or at least a 50 limit has been in the plans since the start.
Built for comfort, not speed.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by RichardA35 »

rhyds wrote: Mon Jun 28, 2021 14:59 Design speed has always been 50mph on the section in question, or at least a 50 limit has been in the plans since the start.
...and rereading the report, its main complainant chooses a 65-70 mile commute of which only about 5-10 miles would be on the road in question so not really affected by a 50 limit given what might occur elsewhere. (They should really get with the programme of lodging away, car share or remote working etc but that's another story)
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by Hdeng16 »

Of all the ridiculous speed limit reductions around the country, this one really doesn't bother me.

People seem to forget that the single or 2+1 sections were narrow and twisty in parts and 50mph was a rarity anyway. 40mph seemed to be the average on a good run and avoiding elephant races.

Stick cruise control on at 50 and enjoy the view!
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by B1040 »

So what we're going to get is a nice reliable DC so safer than S2+1. Traffic will flow smoothly so journey times will be more predictable, and some car drivers will think "I could be going a bit faster here" which happens on many roads.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by fras »

OK, the design assumption was 50 mph, but who sets the standard for 50 mph ? This country is notorious for its extremely nervous attitude to risk, as the continuing Covid19 restrictions show.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by DB617 »

fras wrote: Tue Jun 29, 2021 12:05 OK, the design assumption was 50 mph, but who sets the standard for 50 mph ? This country is notorious for its extremely nervous attitude to risk, as the continuing Covid19 restrictions show.
That would be DMRB, based on geometric and physical calculations and factor of safety (assuming drivers are sometimes less than the 'ideal'..)
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by RichardA35 »

fras wrote: Tue Jun 29, 2021 12:05 OK, the design assumption was 50 mph, but who sets the standard for 50 mph ? This country is notorious for its extremely nervous attitude to risk, as the continuing Covid19 restrictions show.
So I'm assuming you are reasonably familiar with technical papers and concepts, so please take a few minutes to have a read of TD 9/93 (now in a new format) which explains the concepts behind design speed, horizontal curvature, vertical curvature, stopping sight distance etc and how highways are designed.
These issues are not decided on a whim as it is a fairly complex subject and designers always strive for a scheme with no departures from standards but sometimes it is not possible within the budget available or for other physical reasons especially with upgrades of existing infrastructure.
Feel free to come back with any questions and I'll try to answer them or get help from others.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by Bryn666 »

RichardA35 wrote: Tue Jun 29, 2021 13:43
fras wrote: Tue Jun 29, 2021 12:05 OK, the design assumption was 50 mph, but who sets the standard for 50 mph ? This country is notorious for its extremely nervous attitude to risk, as the continuing Covid19 restrictions show.
So I'm assuming you are reasonably familiar with technical papers and concepts, so please take a few minutes to have a read of TD 9/93 (now in a new format) which explains the concepts behind design speed, horizontal curvature, vertical curvature, stopping sight distance etc and how highways are designed.
These issues are not decided on a whim as it is a fairly complex subject and designers always strive for a scheme with no departures from standards but sometimes it is not possible within the budget available or for other physical reasons especially with upgrades of existing infrastructure.
Feel free to come back with any questions and I'll try to answer them or get help from others.
I am a long standing critic of DMRB being gold plated and providing radii and superelevation that wouldn't be out of place at Monza, but I at least understand the rationale behind it. It doesn't take more than a simple trip through the site in question to understand why 50 mph is more than appropriate and adequate for the situation.

A larger scale equivalent, I-70 through the Glenwood Canyon in the USA which spends most of its time in the canyon on viaducts and in tunnels, is only 60 mph, having been increased from 50, after years of observation to draw an evidence base that perhaps 50 was not appropriate.

I certainly wouldn't entrust drivers who claim they can be trusted select a safe speed because who needs experts to select a safe speed - the fact that 1,800 people a year die and 14,000+ are seriously injured as a result of crashes by "good drivers who know what they're doing" says it all. That's before you get to the damage only "whoops, I'm such a good driver I never saw you" type collisions.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by AAndy »

Alderpoint wrote: Mon Jun 28, 2021 13:11
AAndy wrote: Mon Jun 28, 2021 05:45 It was NSL, and NSL all the way from Abergavenny to Hirwaun, on all the 2+1, which was most of it right up to the time the construction began at Dowlais top.
50 repeater here in September 2011.
The tredegar to Dowlais top section began in the early noughties, that was when it was still nsl at clydach gorge and yes, some of clydach had been put into a 50mph zone by 2011, theres a video I put on youtube showing that.. I'll have to look through for another one when little chef was still going at Gilwern.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by fras »

RichardA35 wrote: Tue Jun 29, 2021 13:43
fras wrote: Tue Jun 29, 2021 12:05 OK, the design assumption was 50 mph, but who sets the standard for 50 mph ? This country is notorious for its extremely nervous attitude to risk, as the continuing Covid19 restrictions show.
So I'm assuming you are reasonably familiar with technical papers and concepts, so please take a few minutes to have a read of TD 9/93 (now in a new format) which explains the concepts behind design speed, horizontal curvature, vertical curvature, stopping sight distance etc and how highways are designed.
These issues are not decided on a whim as it is a fairly complex subject and designers always strive for a scheme with no departures from standards but sometimes it is not possible within the budget available or for other physical reasons especially with upgrades of existing infrastructure.
Feel free to come back with any questions and I'll try to answer them or get help from others.
I will have a read, but it doesn't answer the basic question of - who has decided that a set of parameters causes the output of a particular speed limit ? Near me, the new dual-carriageway A5020 link road off the A500 has a limit of 50 mph. This was a local scheme and when I asked my local councillor about the speed limit, he said that he had driven it shortly after it opened, and before the limit was applied, and 50 mph seemed about right. Certainly there is no speeding of any seriousness, as there is a roundabout half-way along and it's less than a mile anyway. I doubt the DMRB was used here, (maybe it was), but the speed limit does seem right, On the other hand the A555 has a lengthy 50 mph section which seems barmy. So it is not all perfection and everything is not the best in the best of all possible worlds.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by roadtester »

When it opens, I'm sure the reaction is going to be more "Wow - how did they manage to squeeze such a good road through here?" not "For crying out loud, why is this only a 50?"
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by RichardA35 »

fras wrote: Tue Jun 29, 2021 21:25 I will have a read, but it doesn't answer the basic question of - who has decided that a set of parameters causes the output of a particular speed limit ?
Basically, the laws of physics.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by Bryn666 »

roadtester wrote: Tue Jun 29, 2021 21:32 When it opens, I'm sure the reaction is going to be more "Wow - how did they manage to squeeze such a good road through here?" not "For crying out loud, why is this only a 50?"
Yes, only in this country do we complain when roads are not built, and then complain when they are.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by rhyds »

RichardA35 wrote: Wed Jun 30, 2021 06:43
fras wrote: Tue Jun 29, 2021 21:25 I will have a read, but it doesn't answer the basic question of - who has decided that a set of parameters causes the output of a particular speed limit ?
Basically, the laws of physics.
That's not really an answer, as the laws of physics have a very different outcome when applied to a 1986 Ford Sierra as opposed to a 2016 Focus, or a Fiesta versus a 44t HGV. How often are the regs updated to take in to account improved vehicle performance?
Built for comfort, not speed.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by roadtester »

rhyds wrote: Wed Jun 30, 2021 10:43
RichardA35 wrote: Wed Jun 30, 2021 06:43
fras wrote: Tue Jun 29, 2021 21:25 I will have a read, but it doesn't answer the basic question of - who has decided that a set of parameters causes the output of a particular speed limit ?
Basically, the laws of physics.
That's not really an answer, as the laws of physics have a very different outcome when applied to a 1986 Ford Sierra as opposed to a 2016 Focus, or a Fiesta versus a 44t HGV. How often are the regs updated to take in to account improved vehicle performance?
Unfortunately, while vehicle performance is improving, driver performance is staying about the same or perhaps even declining!
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by marconaf »

RichardA35 wrote: Wed Jun 30, 2021 06:43
fras wrote: Tue Jun 29, 2021 21:25 I will have a read, but it doesn't answer the basic question of - who has decided that a set of parameters causes the output of a particular speed limit ?
Basically, the laws of physics.
But that isn’t true is it.

As an engineer, there is no immutable law that says a speed for this road is safe or unsafe in the 50-70 region being discussed.

If 70 were somehow unsafe for a standard car to negotiate this road in terms of road-vehicle performance and controllability, it would warrant a limit way below 50. We all know people are going to drive this at 70, just as people drive motorways at 80 and above, and indeed that is tacitly accepted.

Where the line is drawn is inherantly a subjective decision based on risk.

In terms of that risk, the geometry of the road and “physics” is not the driving (hah!) factor here, but an assessment on human interactions is. They may be qauntitative assessments (something I do a lot of in terms of human interactions with vehicle performance and control) but they are not laws of physics.

Fundamentally, our view of humans and risk, is what determines limits - physics is just a starting point. The physics of this road are far better than its predecessor, and indeed, many other roads in the country. Challenging the next applied step is not “Mr Toad wanting to scream down at 135mph” and its a sign of the times (and people’s deficiencies), that any challenge is so often misrepresented as that extreme.

The OP’s point AIUI, is that it is where we go from that starting point - our approach to managing risk, that is wrong. I’m strongly inclined to agree.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by fras »

RichardA35 wrote: Wed Jun 30, 2021 06:43
fras wrote: Tue Jun 29, 2021 21:25 I will have a read, but it doesn't answer the basic question of - who has decided that a set of parameters causes the output of a particular speed limit ?
Basically, the laws of physics.
Having now had a look at "the manual", it seems that the key word is "relaxations". This is where one can deviate from what the formulae come up with. Clearly this is optional, so one does wonder whether the option is ever taken up, because officialdom always likes to be able to say "its all as per the design manual", whereas if one relaxes the standard, you can always be criticised if something untoward comes up later on.
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Re: A465 Heads Of The Valleys Rd Dualling: Gilwern To Brynmawr

Post by Bryn666 »

If all the "the road should be 70" people can explain how you achieve forward visibility around, say, the bend at Brynmawr given there is a solid concrete wall immediately to the right hand side, and allow for an appropriate reaction time to a developing hazard before braking is brought into consideration, I am sure the highway engineers will be all ears.

Armchair engineering on SABRE is getting really boring, because the usual reason for it is "it's so unfair I can't do what I want to do without consequence".
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