Hi Mike,
My experience of airports is confined to inside an aluminium tube.
However, for intersections such as you describe, I can't see any difference
in principle. A constantly changing radius on a clover leaf where you
inevitably have grade changes as well seems just as frightening.
Lastly, as wfb indicated assuming a symmetrical curve, it you have an entry
spiral > 180 degrees, add an exit spiral > 180 degrees and you have gone
through > 360 degrees. I don't think I'd approve that sort of layout. Even
with a circular curve, you would have to wonder if there is a better
solution to the intersection layout.
--
Laurie Comerford
CADApps
www.cadapps.com.au
"Michael Rogerson" wrote in message
news:D6F1B79B06B9F5AB0FC95C4AF0C70053@in.WebX.maYIadrTaRb...
> Hi Laurie,
> Agreed, frightening indeed! Not in roads typically but I have in pratice,
> use a spiral lead-off line on a Runway/Taxiway intersection that was
indeed
> greater than 90 degrees, but not by much.
>
> I'm thinking more along the lines of complex interchanges, cloverleaves,
> snaking viaducts and the sort - if anyone has been held back by this
> limitation.
>
> regards,
> Mike
>
> "Laurie Comerford" wrote in message
> news:37D85D08B8B752274F024B54817BCACD@in.WebX.maYIadrTaRb...
> > Hi Mike,
> >
> > Bearing in mind that a driver has to assess the speed at which they can
> > drive around a curve and to do this they need to be able to see the
curve,
> > it would seem fairly frightening to design a spiral through 90 degrees
let
> > alone 180 degrees.
> >
> > --
> >
> >
> > Laurie Comerford
> > CADApps
> > www.cadapps.com.au
> >
> >
> > "wfb" wrote in message
> > news:3A908D28A84BCD1D7495613993CC077B@in.WebX.maYIadrTaRb...
> > > Is this not similar to having a triangle with more than 180 degrees
> total
> > in
> > > the 3 interior angles?
> > >
> > >
> > > "Michael Rogerson" wrote in
> > message
> > > news:156AE291D93BBE54FA314ED5E220ED1F@in.WebX.maYIadrTaRb...
> > > | Quick question for those of you who use (or have used) alignment
> spirals
> > > in
> > > | real world applications.
> > > |
> > > | As you may know, Land Desktop does not allow creation of a spiral
with
> a
> > > | total deflection angle greater than 180 degrees. There is a
> > mathematical
> > > | reason for this.
> > > |
> > > | Question - Has anyone run into any specific cases where they needed
a
> > > spiral
> > > | with a total deflection angle greater than 180 degrees? If you
have,
> > some
> > > | more detail would be helpful.
> > > |
> > > | Thank you,
> > > | Mike
> > > |
> > > | Autodesk, Inc.
> > > | Michael C. Rogerson, PE
> > > | Product Designer - Program Manager
> > > | ISD Civil Engineering Software Development
> > > |
> > > |
> > > |
> > >
> > >
> >
> >
>
>