Why do they deliberately obscure vision at roundabouts?

[TurboHatchback]

On many roundabouts with dual carriageway approaches there seems to be fences or other visual obstructions put in place for no other purpose I can see but to block peoples view of the traffic until they are right on the roundabout.

Case in point: Google map link

What on earth is the point of these? If one has a good early view of the roundabout it allows one to plan the approach, minimise unnecessary braking or stopping and maximise traffic flow. Obscuring the approach just creates the opposite of the above, it increases unnecessary braking and stopping, reduces traffic flow, wastes fuel etc etc. As far as I can see they are up there with traffic calming measures in the category of truly stupid ideas that somehow seem to have made it to completion.

Does anyone know of any good reason for these features?

[TurboHatchback]

OpulentBob said:

Paragraph 8.8

http://www.dft.gov.uk/ha/standards/dmrb/vol6/secti...

"Excessive visibility to the right can result in high entry speeds, potentially leading to accidents. On dual carriageway approaches where the speed limit is greater than 40mph, limiting visibility to the right by screening until the vehicle is within 15 metres of the give way line can be helpful in reducing excessive approach speeds. The screening should be at least 2m high, in order to block the view of all road users. Screening can also be used on flared approaches on high speed single carriageway roads where there is a long splitter island."

Well that would explain their presence but I'm afraid I retain my opinion that they're a bloody stupid idea. The very concept of "excessive visibility" is an oxymoron with respect to driving, yet more pandering to the lowest common denominator of competence .

Maybe one day someone will be able to foist them with their own petard by explaining that by pointlessly forcing everyone to brake and accelerate constantly they are adding to pollution and CO2 emissions and to save the planet we should remove all 'traffic calming measures', speedbumps and stupid visual obstructions .

[TurboHatchback]

Bennet said:

If they are spending money doing it, it will have been shown to work. They don't spend money just because someone once had a hunch that it might help.

Too many people: "This doesn't imediately make sense to me, therefore it's stupid."

I'm afraid I don't share your fundamental faith in organisations only doing things because they make sense. I see countless examples of quite the opposite.

You are not going to be able to convince me that these make sense. This road is a 30mph limit and would flow freely and safely except some cretin though it would be a good plan to introduce extra traffic jams, contention/danger and pollution for absolutely no benefit to anyone.

[TurboHatchback]

OpulentBob said:

How has that created danger? Is it not big enough and illuminated enough to see?!

Because now you have cars travelling in opposite directions on the same piece of tarmac. Only the other day I saw a learner driver get a priority wrong and go when they should have waited. The car going the other way also went and they nearly had a head-on collision followed by a long stand off whilst they both waited for each other to reverse. People are constantly speeding up just to fit through before someone else and cutting it finely. It also moves attention away from the surroundings and watching out for hazards and onto navigating these obstacles.

OpulentBob said:

I'll bet there was a speeding/rat running issue down there, and kids (?) use the park on the left? Lots of old duffers live on the right (they look like retirement homes)?
Speed humps are a no-no due to houses. Schools, shops, churches etc all down there, which bring substantial problems at their various kicking-out times.

It doesn't actually slow anyone down though, those that sped before do so even more to fit through the gaps and make up time lost, those that didn't still don't. It is a hugely wide road with a very slow limit, when obeying the limit there is practically no risk of people/things jumping out in front of you.

OpulentBob said:

Stop looking for people to blame, because I'd bet a penny to a pound there are serious underlying issues with drivers taking the piss along there.

Not really no but if there were then these do nothing to help the problem.

OpulentBob said:

Nice attitude though, calling the planners cretins. If the scheme doesn't make sense to you, then maybe, just maybe, YOU'RE the thicko.

I would hazard a guess that the actual road planners were told to do something by the council and this was the least intrusive option they could come up with, hence why they are so far apart and serve no purpose at all in actually slowing anyone down. I would honestly rather see speed cameras every 50ft than these things.

BTW, insulting people on the internet doesn't tend to help your argument.

[TurboHatchback]

Rick Cutler said:

Yep I know these were installed a few years ago near Cheltenham on the M5 junction. I have to stop, check then go again. You did have a very good view before plenty of time to work out if you could make it.

https://www.google.co.uk/maps/@51.8895,-2.153844,3...

That is a classic example right there, it would have been a really nice approach without them but now you have to pointlessly waste fuel, time and brake pads instead of just smoothly continuing.

[TurboHatchback]

deanogtv said:

or give little jonny in his saxo vtr enough distance to see there isn't anything coming around the roundabout, give it a little more beans to see if he can take a racing line through the roundabout, clip a kerb and roll his car over and over and then theres no more little jonny.

Trying to protect people from their own stupidity never leads to good legislation though. The situation you describe could be considered natural selection in action. These obstructions won't actually make anyone drive round the roundabout slower, just pointlessly stop then waste fuel getting going again and accelerating up to the same speed they would have been doing anyway. One also needs a larger gap to pull into from stationary than with a rolling start (which one usually has if there is sufficient advanced visibility) so I'm still pretty unconvinced by the argument that it somehow increases traffic flow.

[TurboHatchback]

Cotty said:

TurboHatchback said:

I'm afraid I don't share your fundamental faith in organisations only doing things because they make sense. I see countless examples of quite the opposite.

Do you work for the same company as me?

Possibly .

otolith said:

I wonder if anyone has calculated the increase in CO2 emissions caused by forcing people to drive less efficiently?

I doubt it, those who end up in governmental positions responsible for complaining about CO2 and such don't seem to be troubled by inconveniences such as physics and logic.

[TurboHatchback]

njd27 said:

There is some back story to the barriers in Cadnam. Motorcyclists had noticed that the two roundabouts (the one in your link and the motorway roundabout connected by a 200yd stretch of dual carriageway) contained a very entertaining sequence of bend. It's on the route down to the Poole Quay bike meet, and you can imagine that if every Tuesday night you get 5/10 bikers doing laps of the two roundabouts, the local residents would start complaining.

So they ended up putting in those barriers and cut the speed limit from 70 to 50mph.

You can get a gist of it if you search for Cadnam GP Circuit

Edited by njd27 on Wednesday 23 April 11:44

Ah, I see. It seems that most people at the time when they were put up thought the same as me (i.e. that it was a stupid idea). Obviously bikers doing laps is not ideal from a safety perspective but IMHO these make it more dangerous not less. The 50mph limit is ok as the section is so short but the barriers are .