Unsafe roundabout design - North East

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Peter Freeman
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Re: Unsafe roundabout design - North East

Post by Peter Freeman »

FosseWay wrote: Mon Jun 14, 2021 13:57 ... There are a number of issues with mandating that drivers must leave the roundabout in the right-hand of two available lanes after turning right.
It's not mandated in AU. Perhaps I should have said that the video 'advises'.
Some of them admittedly may be more likely to be an issue in the UK than Australia given the tendency towards broader roads with more room in all directions in Aus.
I don't think so. The issues are the same. While your suggested 'tendency' is somewhat true, our road dimensions, lane widths, etc, are the same.
1. In the case of the green car in the HC example above, it shouldn't matter which exit lane it takes because there shouldn't be anything alongside once it's passed the straight-on exit.
If lane usage custom permits, why shouldn't there be? This is part of my point. A car that enters alongside another would know or first determine which exit the approaching car is aiming for and whether it's going to exit in the right lane. It would then either proceed, with caution, or wait.
People shouldn't be turning right from the left lane.
We don't turn right from the left lane.
and people shouldn't be setting off from the left arm at the same time as someone already on the roundabout is still passing the entrance.
The main point of my post is that, with consistent lane discipline, it is possible for such setting-off to be safe. The vehicles travel side-by-side, and merge after exit if applicable.
3. Urban areas in Britain are often not particularly planned, with several turns in quick succession. It's entirely possible for there to be a left turn a few tens of metres after the right-hand exit from that roundabout, and if you want to take that exit, you need to be in the left lane. The requirement to position yourself in good time for your intended manoeuvre doesn't suddenly not apply just because the stretch of road immediately before your turn happens to include a roundabout. As I say, this kind of crowded layout may be less of an issue in Australia.
You have an idealised image of AU's urban roads! I can assure you that most of the peculiar configurations that you encounter in the UK do also occur in Australia. Our inner urban areas are old and fairly dense.
4. I'm not aware that there is a concerted tendency to tell people on the approach to a roundabout how many lanes the exit has, especially exits other than the main line (usually straight on). In other words, a driver approaching the roundabout to turn right won't know how many lanes there are on the exit road till they see it, after passing the straight ahead exit.
This is so in AU too, although we don't have giant roundabouts so there is better overall visibility.
A related point is that there are plenty of roundabouts with two lanes, where less major exits off them only have one. This rule then essentially requires them to exit the roundabout from the outside lane, which I would have thought is contrary to both the HC and common sense.
Road markings and signage specific to each roundabout and common sense take care of both these issues, as in the UK. And it's not a "rule".
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FosseWay
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Re: Unsafe roundabout design - North East

Post by FosseWay »

Peter Freeman wrote:In contrast, the on-line highway-code-equivalent in Australia (Victoria) explicitly instructs a lane-disciplined exit from such a roundabout.
I'm not sure how you're supposed to interpret "explicitly instructs" as anything other than an explicit instruction!

And regarding the difference between UK and Aus, I did say that the difference in recommendation *may* depend on general road differences. I was basically offering a possible explanation of why a recommendation that evidently works in Australia I don't think would in the UK.

I really don't see the problem with moving over to the left before turning left. It is normal behaviour in other circumstances. On larger roundabouts with multilane exits, any departure from that basic premise is explained on signs and/or written on the tarmac. The HC recommendation is for "default" roundabouts where no location-specific instruction is provided.
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Peter Freeman
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Re: Unsafe roundabout design - North East

Post by Peter Freeman »

Sorry - I didn't word that well. I didn't intend to give the impression that right lane exit from a roundabout was mandatory.
FosseWay wrote: Mon Jun 14, 2021 13:57 4. I'm not aware that there is a concerted tendency to tell people on the approach to a roundabout how many lanes the exit has, especially exits other than the main line (usually straight on). In other words, a driver approaching the roundabout to turn right won't know how many lanes there are on the exit road till they see it, after passing the straight ahead exit.
Although they are used only at complex or unusual roundabouts, signs such as this in AU provide guidance. They specifically show the number of lanes and where each one goes to. They encourage efficient parallel usage within roundabouts, and side-by-side entry and exit. The driver behaviour naturally trickles down to include locations where such signage is not provided.

https://www.google.com.au/maps/@-34.927 ... 384!8i8192
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FosseWay
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Re: Unsafe roundabout design - North East

Post by FosseWay »

Peter Freeman wrote: Tue Jun 15, 2021 12:29 Sorry - I didn't word that well. I didn't intend to give the impression that right lane exit from a roundabout was mandatory.
FosseWay wrote: Mon Jun 14, 2021 13:57 4. I'm not aware that there is a concerted tendency to tell people on the approach to a roundabout how many lanes the exit has, especially exits other than the main line (usually straight on). In other words, a driver approaching the roundabout to turn right won't know how many lanes there are on the exit road till they see it, after passing the straight ahead exit.
Although they are used only at complex or unusual roundabouts, signs such as this in AU provide guidance. They specifically show the number of lanes and where each one goes to. They encourage efficient parallel usage within roundabouts, and side-by-side entry and exit. The driver behaviour naturally trickles down to include locations where such signage is not provided.

https://www.google.com.au/maps/@-34.927 ... 384!8i8192
That is useful extra information, I agree, in cases where there "genuinely" are two (or more) lanes at an exit from a roundabout. I also agree that on major roads where there are two lanes on approach, two lanes on the roundabout and two lanes on the exit, it makes sense to stay in the same lane throughout the manoeuvre.

But many UK roundabouts have, for reasons that escape me, tiny sections of nominal two-lane exit before it reduces to one again. Ideally you don't want to be in the outer lane here, especially given the typical British "this is my lane, sod off" behaviour at lane merges. In all practical senses, such exits have one lane, and if the roundabout has two, you need to be in the left of those two in order to exit, as with any other exit from a mainline.
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Debaser
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Re: Unsafe roundabout design - North East

Post by Debaser »

FosseWay wrote: Tue Jun 15, 2021 14:06 But many UK roundabouts have, for reasons that escape me, tiny sections of nominal two-lane exit before it reduces to one again. Ideally you don't want to be in the outer lane here, especially given the typical British "this is my lane, sod off" behaviour at lane merges. In all practical senses, such exits have one lane, and if the roundabout has two, you need to be in the left of those two in order to exit, as with any other exit from a mainline.
CD116 Geometric design of roundabouts wrote: 3.28.1 The exit width for normal roundabouts should accommodate one more traffic lane than is present on the link downstream.

3.28.2 At a normal roundabout, if the downstream link is a single carriageway road, the exit width should be between 7 metres and 7.5 metres and the exit should taper down to a minimum of 6 metres.

NOTE The additional width allows traffic to pass a broken down vehicle.

3.28.3 Where the downstream link is a single carriageway road, the exit width should reduce at a taper of 1:15 to 1:20, starting at the end of the exit from the roundabout, ensuring 6 metres at end of traffic island, to avoid exiting vehicles encroaching onto the opposing lane at the end of the traffic island.
It's because the DMRB is paranoid that vehicle breakdowns are most likely to happen adjacent the splitter islands on the exits from roundabouts, which would obviously cause the sky to fall in.
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Re: Unsafe roundabout design - North East

Post by FosseWay »

Extra *width* I don't have a problem with; it also allows some wiggle room for larger vehicles. But why mark two lanes for a couple of car lengths? It's just inviting the mutually antagonistic behaviours of the "must-get-in-front" impatient so-and-so and the "nearside lane has priority so I'll close all available space down" wannabe enforcer.
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