Fences to decrease visibility at roundabouts

[Hooli]

andygo said:

I detest those rumble strip things, play havoc when you are on 40 profile tyres.

And similarly thick is that high grip red tarmac they put down before some zebra crossings. Great idea, but why stop 2 meters before the actual crossing.

Imagine, hard on the brakes, gonna stop before hitting the kid, lots of grip, oops, its all gone, kid splatted for the sake of a bit more high grip... Barmy.

And whats worse is when it wears away, so you have variable grip. If it was a good idea originally, just maintain it please.

Why oh why do they start this stuff AFTER the beginning of the bend & before the end? You turn in, squirm as the grip changes & then again on the exit. Very disconcerting & occasionally worrying on a bike when the front wheel slides as you come off it.

[stuart313]

SHutchinson said:

One possible benefit that I believe these barriers have is that a lot of drivers would approach a roundabout at speed and just look to see if there was an object the size of a car approaching from the right. If they couldn't see one in their field of view they might assumme that the roundabout was clear and not adjust their speed before joining the roundabout. I can imagine a situation where this may lead to a slow moving road user (cyclist etc.) almost directly infornt of the vehicle being completely overlooked. The barriers being there prevents this as the approaching driver can only look forward to check if it's safe to proceed.

I will admit to coming within a couple of centimetres of taking out the postman doing this on a roundabout, I was actually on the way to the depot to collect a parcel and ironically I had to drive even faster to make sure I collected it and was out of there before he got back.

Also what happens when a big lorry behind you can see quite clearly that there is nothing coming round yet you have to stop to look. Its a common type of accident anyway at the best of times without an added complication.

Edited by stuart313 on Tuesday 28th April 18:47

[Guybrush]

Idiotic. Congestion-creating idea. Interrupts smooth flow.

[Ayahuasca]

By the same logic they should ban street lights and car headlamps.

[MBBlat]

I may be wrong (cue 200 posts telling me that I am) but I thought that one of the reasons for these was to stop the type of accident where the 2nd car in line saw a large gap, assumed that the first driver would go for it, only to drive straight into the back of the hesitant/cautious driver in front.

[Dammit]

We'll have no reasoned, logical thought here!

[Phatboy317]

Swervin_Mervin said:

Phatboy317 said:

Swervin_Mervin said:

It's generally found these days that the less visibility you have, the safer a junction is likely to be.

By whom? Can you back up that assertion?

One example - try reading Manual for Streets and Manual for Streets 2. Visibility requirements at t-junctions were significantly relaxed in recent years and the evidence base for doing so found just that.

It doesn't show that reducing visibility improves safety, merely that reducing visibility increases perceived danger, which in turn makes people slow down (no st, Sherlock) and they then simply assume that this improves safety - ignoring the fact that reduced visibility increases actual danger, not just perceived danger.

[Terminator X]

Kind of makes sense as you need to slow down to see what's coming but in reality just annoying making you slow down often for no reason.

TX.

[Phatboy317]

Terminator X said:

Kind of makes sense as you need to slow down to see what's coming but in reality just annoying making you slow down often for no reason.

TX.

It's not simply slowing down, as much as having to come to a complete stop.
And then you either have to accelerate like a scalded cat to get up to speed before the next vehicle comes around the bend, or stand there waiting a very long time for a suitably large gap.

[Toltec]

It is more a mitigation than prevention system, the collision happens at lower speed so reducing injuries.

Though to be fair it probably also turns minor bumps into near misses so while still basically mitigating mistakes it could lower actual collisions.

[Dammit]

Watch out, you've suggested that lower speeds mean less severe RTA's - prepare for a torrent of denial, including ridiculous suggestions to leave three seconds before you actually did in order to be able to drive everywhere as though your trousers are on fire in perfect safety.

[Phatboy317]

Toltec said:

It is more a mitigation than prevention system, the collision happens at lower speed so reducing injuries.

It reduces the speed of the traffic entering the roundabout down to a virtual stop, while doing little or nothing to slow down the traffic actually on the roundabout.
This will tend to increase the speed differential rather than reduce it.

[Dammit]

But if it avoids accidents that would otherwise have occurred then the speed differential is totally meaningless in terms of safety.

[Toltec]

Dammit said:

Watch out, you've suggested that lower speeds mean less severe RTA's - prepare for a torrent of denial, including ridiculous suggestions to leave three seconds before you actually did in order to be able to drive everywhere as though your trousers are on fire in perfect safety.

Lower impact speeds do reduce injuries, that is just physics, however the initial travelling speed is not so tightly linked.

[Toltec]

Phatboy317 said:

It reduces the speed of the traffic entering the roundabout down to a virtual stop, while doing little or nothing to slow down the traffic actually on the roundabout.
This will tend to increase the speed differential rather than reduce it.

It will vary depending on the situation, however it could slow traffic on the roundabout as vehicles will need to accelerate rather than enter at a higher speed.

It would be more correct to say the energy is reduced, differential speed is not that precise as you are also dealing with vectors.

In case it is not clear, I do not like the barriers as I can drive properly. That does not preclude understanding why they can appear effective. The best way to defeat measures like this is to understand why they are used.

[Phatboy317]

Toltec said:

Phatboy317 said:

It reduces the speed of the traffic entering the roundabout down to a virtual stop, while doing little or nothing to slow down the traffic actually on the roundabout.
This will tend to increase the speed differential rather than reduce it.

It will vary depending on the situation, however it could slow traffic on the roundabout as vehicles will need to accelerate rather than enter at a higher speed.

It would be more correct to say the energy is reduced, differential speed is not that precise as you are also dealing with vectors.

In case it is not clear, I do not like the barriers as I can drive properly. That does not preclude understanding why they can appear effective. The best way to defeat measures like this is to understand why they are used.

They seem to take it as a given that slowing the traffic down - by any means - improves safety. I would question this.

There's no hard evidence that they are actually effective - but merely the assumption that they improve safety by reducing speeds.

Reduced visibility reduces safety margins - I may be wrong, but in the absence of hard evidence to the contrary, I don't think so.

Edited by Phatboy317 on Tuesday 28th April 22:50

[Toltec]

Phatboy317 said:

There's no hard evidence that they are actually effective - but merely the assumption that they improve safety by reducing speeds.

Reduced visibility reduces safety margins.

Someone above mentioned a reduction in accidents, are you saying that you have data that shows there is no such effect? Would be good if you have, proves the point.

While again I agree with your second point personally, we are dealing with the scope of human nature here so the situation is not that simple. Things that would make roads safer and free flowing for good drivers will not work for most, unfortunately techniques that work for the lcds do not make good drivers less safe. Finding the balance is not easy.

[HTP99]

In the summer just gone, the Council in my area; Surrey, planted a lot of those fast growing seasonal meadow type flowers that attract butterflies and bees, on roundabouts, approaches to roundabouts and also junctions.

These flowers got so tall that in some instances you had no alternative than actually coming to a complete halt and then having to edge out to see if the way was clear; very dangerous.

[Gareth79]

Dammit said:

We'll have no reasoned, logical thought here!

And people bringing their so-called "facts" and "research" on the internet, when it's "obvious" they are bad

[RyanOPlastry]

MBBlat said:

I may be wrong (cue 200 posts telling me that I am) but I thought that one of the reasons for these was to stop the type of accident where the 2nd car in line saw a large gap, assumed that the first driver would go for it, only to drive straight into the back of the hesitant/cautious driver in front.

Some years ago, a local roundabout had earth mounds installed to reduce visibility. Unfortunately there are a number of distribution depots nearby and lots of HGVs. It had the opposite effect, The HGV driver could see that there was nothing coming, and ran into the back of the car in front which had slowed due to no visibility.