AutoCAD Civil 3D General Discussion

AutoCAD Civil 3D General Discussion

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Valued Contributor
whalen.jon
Posts: 56
Registered: ‎05-12-2006
Message 1 of 16 (308 Views)

Roundabouts

308 Views, 15 Replies
01-27-2009 12:34 PM
Hi there. I have a question, however, not related to Civil 3D. It's more a general question regarding roundabout design. When it comes time to create your entry curves, what steps do you guys generally follow? The US DOT (FHA) guide talks about the splitter island entry curve being tangential to the central island, and the outside entry curve being tangential to the ICD (as do many other guides I've looked at). Of any of you who have designed roundabouts before, do you aim to keep the two said entry curves concentric with each other? If so, how do you keep them tangential and concentric when your entry width (5.3m) is not the same width as your circulatory width (6.3m) on an ICD of 40m? This is a single-lane, four-legged roundabout. I've never designed one before, and I'm having a lot of fun with it. The approaches are 50km/h. Capacity isn't a big issue, as they're local roads (very low volume of traffic).

Thanks,

Jon
Distinguished Mentor
castled071049
Posts: 823
Registered: ‎11-15-2005
Message 2 of 16 (307 Views)

Re: Roundabouts

01-27-2009 05:24 PM in reply to: whalen.jon
You can't have them concentric and tangential with different incidental curves. Forget concentricness. Make them tangential. The roundabout needs to have travel lanes wider than the approach lanes. Do this and it will work out fine.
Valued Contributor
whalen.jon
Posts: 56
Registered: ‎05-12-2006
Message 3 of 16 (307 Views)

Re: Roundabouts

01-28-2009 04:51 AM in reply to: whalen.jon
Thanks. I figured that...
Suppose you have different radii for your inner and outer curves (tangential and not concentric) - do you aim for a nice even entry/exit width (of say 5.3m exactly)? Or do you take what you end up with so long as it accommodates your design vehicle, meets your capacity requirements and meets safety requirements? Or do you work with different radii's/flaring so you do indeed end up with your desired entry/exit width?
I must apologize if I'm asking 'rookie' questions, but I'm a very detailed oriented person ;-) .

Thanks again!
*Laurie Comerford
Message 4 of 16 (307 Views)

Re: Roundabouts

01-28-2009 01:24 PM in reply to: whalen.jon
Hi whalen,

The best approach to this issue is to use a program like Autotrack to
drive your design vehicle through the roundabout. You can then adopt
any combination of curves which meet the requirements of:

Being easy to draw
Being easy to set out
Having a smooth appearance from a driver's viewpoint
Meet any design parameter requirements of an approval Authority

This way the functional requirements of the design will be met, rather
than a compliance with a difficult to specify and interpret set of rules
about relative radii, widths at certain locations etc.

Regards


Laurie Comerford

whalen.jon@gmail.com wrote:
> Thanks. I figured that... Suppose you have different radii for your
> inner and outer curves (tangential and not concentric) - do you aim for
> a nice even entry/exit width (of say 5.3m exactly)? Or do you take what
> you end up with so long as it accommodates your design vehicle, meets
> your capacity requirements and meets safety requirements? Or do you work
> with different radii's/flaring so you do indeed end up with your desired
> entry/exit width? I must apologize if I'm asking 'rookie' questions, but
> I'm a very detailed oriented person ;-) . Thanks again!
Distinguished Mentor
castled071049
Posts: 823
Registered: ‎11-15-2005
Message 5 of 16 (307 Views)

Re: Roundabouts

01-28-2009 04:00 PM in reply to: whalen.jon
Sorry to take so long to respond. Have been very busy lately. Basically, I don't get too fancy with it. I use whatever radii are necessary to make them tangential with the concentric circles of the roundabout (paying attention, of course, to recommended lane sizes and roundabout diameters from the guide books). Then I use AutoTurn to drive the biggest expected vehicles through the roundabout to make sure that it functions properly. If it works and looks pretty, then it's a go for me.
*Expert Elite*
mikeevans
Posts: 760
Registered: ‎09-29-2008
Message 6 of 16 (307 Views)

Re: Roundabouts

01-29-2009 03:57 AM in reply to: whalen.jon
Interesting: Does the US design of roundabouts not use traffic flow analysis at the entries and exits of the roundabouts to obtain required geometry values.

The UK design relies on these widths to reduce or increase the flow of vehicles through a roundabout and thus safety.

Design elements such as tapers and widening at the entries and exits are fixed by calculations made in software which evaluates the traffic flows from each leg and then gives the required geometry constraints, entry/exit curve radius, flare lengths and tapering widths.

If not I want to design roundabouts in the US : )
Mike Evans

Civil3D 2013 / 2014 British UK
Windows 7 Professional 64-bit
Intel(R) Core(TM) i7-3820 CPU @ 3.60GHz (8 CPUs), ~4.0GHz With 32768MB RAM, AMD FirePro V4900, Dedicated Memory: 984 MB, Shared Memory: 814 MB

Distinguished Contributor
dlmanning
Posts: 109
Registered: ‎12-06-2007
Message 7 of 16 (307 Views)

Re: Roundabouts

01-29-2009 05:58 AM in reply to: whalen.jon
http://www.civil3d.com/2008/10/3d-models-replaced-by-cones/

I think this answers your questions about the states.
Valued Contributor
whalen.jon
Posts: 56
Registered: ‎05-12-2006
Message 8 of 16 (307 Views)

Re: Roundabouts

01-29-2009 06:08 AM in reply to: whalen.jon
Thanks all for the replies.

Having read through volumes of guides, I am simply curious what steps others take from a detailed design point of view for clarification of finer details that the numerous guides don't specifically state.

At this particular intersection, the size of the roundabout will handle the current and projected traffic flows (residential area). I'm using suggested minimum radii's to start and an I-Bus as my design vehicle (14m from TAC - btw, I'm in Canada). As far as the values for the rest of the components, I'm following what the guides suggest, and in the end will obviously ensure a safe and operational roundabout.

My prelim design has since been peer reviewed by an experienced firm, and the changes they suggested are minor, so I know I'm on the right track.

MIKEEVANS, may I ask what software package you are referring to? Is it RODEL?

Thanks everyone,

Jon
*Ian McGregor
Message 9 of 16 (307 Views)

Re: Roundabouts

01-30-2009 05:24 AM in reply to: whalen.jon
ARCADY is the standard roundabout capacity calculation software in the UK.

http://www.trlsoftware.co.uk/products/detail.asp?aid=1&c=1&pid=66

I believe TRL in the UK were the originators of the maths behind RODEL and
the two are still somewhat related, though if I understand it correctly
ARCADY has had the greater amount of ongoing development and is a full
Windows program, whereas I think RODEL is still DOS based? (might be wrong
there)

Regards

Ian

EMIA Product Manager
Autodesk AEC Division


wrote in message
news:6114093@discussion.autodesk.com...
Thanks all for the replies. Having read through volumes of guides, I am
simply curious what steps others take from a detailed design point of view
for clarification of finer details that the numerous guides don't
specifically state. At this particular intersection, the size of the
roundabout will handle the current and projected traffic flows (residential
area). I'm using suggested minimum radii's to start and an I-Bus as my
design vehicle (14m from TAC - btw, I'm in Canada). As far as the values for
the rest of the components, I'm following what the guides suggest, and in
the end will obviously ensure a safe and operational roundabout. My prelim
design has since been peer reviewed by an experienced firm, and the changes
they suggested are minor, so I know I'm on the right track. MIKEEVANS, may I
ask what software package you are referring to? Is it RODEL? Thanks
everyone, Jon
*Expert Elite*
mikeevans
Posts: 760
Registered: ‎09-29-2008
Message 10 of 16 (307 Views)

Re: Roundabouts

01-30-2009 05:47 AM in reply to: whalen.jon
Yep, Arcady is the one I was referring to although I believe we have used Rodel recently. It does fully work from through the command line in WinXP. Thanks Ian, I couldn't remember the name.

I don't actually use it now but have done before, we normally sub to someone else to give us the details.

PS: Does anyone know how I can change my name to lower case or Sentence case. It seems to have got stuck on upper case since I logged on a while ago with caps lock on. : )
Mike Evans

Civil3D 2013 / 2014 British UK
Windows 7 Professional 64-bit
Intel(R) Core(TM) i7-3820 CPU @ 3.60GHz (8 CPUs), ~4.0GHz With 32768MB RAM, AMD FirePro V4900, Dedicated Memory: 984 MB, Shared Memory: 814 MB

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