Bedford turbo roundabout - it is done

[drossall]

Again not really comparable, but I thought this was interesting about the Elephant & Castle.

[Bicycler]

I know of at least two examples in the UK where give way markings are used on the road carriageway where it meets a shared use facility. The shared use facility really ought to be set further from the roundabout. IMO, there should be room fro at least one car to wait for the cycle path, off the roundabout.

I think someone (Pete Owens?) said upthread that cycle lane priority is only permitted where traffic flows are low

[admin]

Regarding the word "Turbo," I presume this is just presentation. (Even I think it's too corny to dismiss the word "turbo" as spin.) They want to give the idea of speed, as in turbo-jet.

I think the allusion is that the roundabout has "blades" a bit like a turbocharger turbine or compressor, which forces traffic on the roundabout to take a fixed route: motorists have to get into the correct lane before they enter the junction, and then they can't change their minds.

The benefit of this design is that vehicles entering the roundabout know where the vehicles on the roundabout already are going. Unlike a non-turbo roundabout where you have to guess which exit a vehicle on the roundabout might use, and thus whether you need to give way to it or not. On a major ordinary roundabout this decision-making can be very difficult, and if you get it wrong there's a crash. So motorists tend to wait and give way when in fact they didn't need to, just in case.

The narrower lanes, and lack of ability to cut corners, also help to reduce speeds a little compared to the same-sized ordinary roundabout.

It's the kerbs on the circulating lanes, that force vehicles to get into the correct lane before they enter the roundabout, and which ensure that everyone knows where everyone else is going, that are key to a proper turbo roundabout. It's a design for improving safety for motor vehicles, as well as increasing roundabout motor traffic capacity for a given space.

[AlaninWales]

The narrower lanes, and lack of ability to cut corners, also help to reduce speeds a little compared to the same-sized ordinary roundabout.

l'll put Chris' image up again:

I repeat, bottom left to top left: shallow corners, no need to cut anything, once you've finished checking over your shoulder that no motor is coming from bottom right, there is no threat - you are pointed at your exit and can get your foot down (please, look at the angle the 'give way' line meets the road edge, that is not going to slow anyone who doesn't want to).

Top right to bottom right, barely more, top left to top right, ditto: There are routes through there you'll need to slow a bit for, but at least three (and the first named appears to be the most major) allow uninterupted speed if there is no motor in the lane you are entering!


Cyclist you say? Pedestrian on the crossing? SMIDSY

[reohn2]

AlaninWales
Horses,water,you can lead them to it,they'll recognise it as such but,they'll please themselves if they drink or not

[Pete Owens]

A curving constrained lane that forces you to more or less hug the island of the roundabout. You turn turn through 120 degrees with a 15m radius. Not as tight as the intital turn on to the roundabout, but enough to keep motor speeds down to cycling speed.

Now please read what I wrote:

If approaching from bottom left and exiting top left, I see a normal UK giveway line,

Not the turns you are describing, but the ones that do not alter at all significantly from current (thanks mjr)

Bottom left to top left, top left to bottom right (specifically does not hug the r'bout).

And those curves also serve to reinforce the point I am making about the much tighter geometry acting to slow traffic to cycling speed.

First the one on the Left (NE-SW).
Before (the pink track): Drivers bend slightly to the left before they reach the junction. As soon as they see the path is clear they enter the roundabout at a tangent - with no deflection at all. Through the roundabout they follow a gentle curve to the right (about 50 degrees with a radius of about 40m) on a wide unconstrained lane, then exit at a tangent and take a gentle curving path on the exit road. Nothing in that geometry that would require drivers to slow much below the speed limit and wouldn't even be noticed as much of a bend if there was no junction there.
After (the green track): Drivers approach the roundabout at right angles. On entry they have to make a tight (50 degree 10m radius) turn left to join the circulating lane - they then have to swing the wheel to the right to follow round the edge of the roundabout (100 degrees 20m radius which is still half the radius as the existing line). Then they need to turn left (50 degree 15m radius) to exit.

Now the one on the right (S-NW).
Before (the pink track): This is simply a very gentle curve of about 30 degrees starting well before the junction and continuing well beyond it. Just looking at the pink line in isolation, you would not be able to deduce where the roundabout is or what radius it has or even that there was a junction at all. The line would not be out of place on a national speed limit A road and the roundabout does not require any deflection whatsoever - at no point are you actually following a circulating line to the right.
After (the green track): Again you approach perpendicular to the roundabout so do not start turning till you reach the junction. The line is as tight as the one described above - but is a bit shorter as it does not follow the roundabout as far. Then you make a 50 degree left turn onto roundabout - follow the line to right round the edge of the roundabout for 70 degrees and then another 50 degree turn to exit.

This second is the movement through the junction where the improved geometry will have the greatest benefit.

[Tonyf33]

if you think for one second that the angles on that roundabout slow traffic down to 'cycling speeds' you're sadly mistaken unless you think that 20mph+ is defined as cycling speed?

whatever the angles I can tell you for nothing that a car can easily drive around the tighter of the turns at 25+mph without braking sweat..that may or may not be the norm but it is easily achievable, to think speeds are going to be reduced at all/in a significant way then you clearly believe the garbage being spouted here, i find that more than a little bit sad and equally annoyed & frustrated that people can be duped so easily

[Pete Owens]

Have you ever driven a car?

To take a 15m radius bend at 20mph involves a lateral acceleration of about half g. That is almost as much as the emergency braking deceleration used to calculate stopping distances in the highway code. And it is not just one bend but a left-right-left combination within a constrained lateral space. 25mph would be out of the question - you would need to be pull 0.8g - ie beyond the ability of your tyres to grip the road!

Here's a short tutorial from a numerate biker:
http://www.stevemunden.com/leanangle.html

[thirdcrank]

As this is a cycle-safety scheme, perhaps we can summarise the anticipated benefits in that connection.

Cyclists who currently ride illegally on the footway will be able to do so legally, which is probably safety-neutral for cyclists. Pedestrian crossings - where mounted riders have no priority over traffic, and where riding a pedal cycle is against the advice of the Highway Code - will have signs of an undecided type: it is hoped they may be specially-authorised CYCLISTS GIVE WAY signs, but the more usual CYCLISTS DISMOUNT signs may be unavoidable. In terms of safety, it is known that such crossing points are the locations of greatest danger to cyclists and the potential confusion is unlikely to increase safety.

There will be increased management of traffic on the actual turbo roundabout in that design speeds will be reduced and drivers will be encouraged to use the specific lane for their intended exit. It is anticipated that the safety of on-carriageway cyclists will be improved by the slower traffic speed and increased predictability of traffic movement. (Doubts have been expressed over the possible effects on cyclists of the raised plastic lane-markers.)

There are differing opinions about whether the availability of a prominently-signed shared use will affect the attitudes of drivers and even the police towards riders using the carriageway (against the advice of the HC.)

This has scheme been described in a CTC statement as a "compromise."
....................................................
Admin

I think there may be concern that the alternative names eg spiral, might cause comments about "ever-decreasing circles." While I'm on, I prefer to avoid assigning human characteristics to motor vehicles: keeping a look out and driving safely is the responsibility of their drivers.

[Tonyf33]

Have you ever driven a car?

To take a 15m radius bend at 20mph involves a lateral acceleration of about half g. That is almost as much as the emergency braking deceleration used to calculate stopping distances in the highway code. And it is not just one bend but a left-right-left combination within a constrained lateral space. 25mph would be out of the question - you would need to be pull 0.8g - ie beyond the ability of your tyres to grip the road!

Here's a short tutorial from a numerate biker:
http://www.stevemunden.com/leanangle.html

it is the left turns and straight ons that are the problem here with regard to speed as you full well know, the constrains of the lanes don't make enough if any difference. I know from experience of having driven through similar & despite high density traffic the speeds are hardly effected and are far above average cycling speeds.

But carry on with your notion that this heap of turd serves any appreciative 'safety' purpose for cyclists never mind that it won't increase cycling and those opting to use the 'pathways' if being co-erced to them from the road will be massively delayed, never mind that this pile of poop will no doubt be 'supported' by CTC et al in other parts of the country for fear they'll lose funding for 'cycling'.
You and your ilk are nothing more than yes men and if you truly think this is making cycling better then more fool you, howver it is the likes of you that will forever leave us 'in the gutter' so to speak.. carry on as you were, I'm done here with this abortion

EDIT to add, as a driver of 21 years I've driven in the most hazardous conditions & also driven as a daily commuter into & around London and other high density traffic for 8 years solid before jacking it all in, so I think my real world experience of what happens at roundabouts and other haphazard/poorly designed rubbish like this is more informed than hypothetical scenarios...

[AlaninWales]

Have you ever driven a car?

To take a 15m radius bend at 20mph involves a lateral acceleration of about half g. That is almost as much as the emergency braking deceleration used to calculate stopping distances in the highway code. And it is not just one bend but a left-right-left combination within a constrained lateral space. 25mph would be out of the question - you would need to be pull 0.8g - ie beyond the ability of your tyres to grip the road!

Here's a short tutorial from a numerate biker:
http://www.stevemunden.com/leanangle.html

Less of the "Have you ever driven" sarcasm please! You do realise that a motorbike has only two small contact patches and cannot corner as fast as a car? (see, it only achieves the same in response).

Here's a roundabout with a less-than 15m radius: http://goo.gl/maps/HxrZz
It is perfectly easy to go from Tanerdy to Abergwili at 30mph; when there is no traffic waiting it feels perfectly natural. I have been overtaken beside the traffic islan in the entrance to Bronwydd Road, because the other car did notlike the 25mph that I was driving at: That is, he had to take an even tighter line, with narrower space than anything on your plan and he managed to squeeze past my car whilst accelerating from 30mph upwards.

[Tigerbiten]

If you look at it objectively, without all the vitriol, what the designers are hoping for is to use the lane dividers to turn a single two lane roundabout into two single lane roundabouts.

So if your a confident rider and take your lane, in theory you shouldn't get under/overtaken once you're on the roundabout due to the lane dividers, so you'll slow traffic down to your speed and the risk should be a lot lower.
The only interesting bit, if you don't know the area, will be getting into the correct lane around where the zebra crossing are.

If you are a pavement cyclist then it becomes legal.
The zebra crossing may encourage you to take more risks crossing the carriageway but then again car drivers see the zebra so they start to think they may have to stop for you.
So it's a bit more 50/50 with this group.

The only group that gets really putout is the gutter huggers.
Due to the lane dividers they won't be able to do this around this roundabout.
So they will either have to take the lane on the way in or take to the pavement.

[Tonyf33]

The zebra crossing may encourage you to take more risks crossing the carriageway but then again car drivers see the zebra so they start to think they may have to stop for you.
So it's a bit more 50/50 with this group.
.

That's the problem though, stats shown earlier in this thread indicate that motorists aren't that keen to let cyclists over zebra crossings even when dismounted, massively less so when they see them cycling along. Take into account the design of the 'turbo' roundabout that is supposed to allow vehicles being closer to each other then you have less chance than ever of the first or even second vehicle stopping. Want to turn right as a path cyclist then you have 4, read 4 seperate zebra crossings to negotiate..because that'll take no time at all when it's busy

[gaz]

Want to turn right as a path cyclist then you have 4, read 4 seperate zebra crossings to negotiate..because that'll take no time at all when it's busy

Right now, without the scheme, as a pedestrian or path cyclist you have 4, read 4 separate totally uncontrolled crossings to negotiate. How will Zebras make such crossings take longer or become more dangerous?

[Psamathe]

I would have thought if you want to slow down the traffic, put up loads of 20 speed signs and loads of cameras. And you will rake in loads on money until all the Clarkson fans lose their licences. Much cheaper and word about cameras and fines will quickly get around and people will mostly slow down (and the speedaholics that don't wont slow down for the proposed scheme anyway).

Ian