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*Rogerson, Michael

# Spirals >180 Deg Deflection Angle

122 Views, 6 Replies
11-06-2003 03:35 AM
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

Thank you,
Mike

Autodesk, Inc.
Michael C. Rogerson, PE
Product Designer - Program Manager
ISD Civil Engineering Software Development
*wfb

# Re: Spirals >180 Deg Deflection Angle

11-06-2003 04:30 AM in reply to: *Rogerson, Michael
Is this not similar to having a triangle with more than 180 degrees total in
the 3 interior angles?

"Michael Rogerson" wrote in message
| 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
|
|
|
*Comerford, Laurie

# Re:

11-06-2003 05:21 AM in reply to: *Rogerson, Michael
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

"wfb" wrote in message
> Is this not similar to having a triangle with more than 180 degrees total
in
> the 3 interior angles?
>
>
> "Michael Rogerson" wrote in
message
> | 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
> |
> |
> |
>
>
*Rogerson, Michael

# Re:

11-06-2003 05:40 AM in reply to: *Rogerson, Michael
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
> 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
>
>
> "wfb" wrote in message
> > Is this not similar to having a triangle with more than 180 degrees
total
> in
> > the 3 interior angles?
> >
> >
> > "Michael Rogerson" wrote in
> message
> > | 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
> > |
> > |
> > |
> >
> >
>
>
*Rizzo, Jon

# Re:

11-06-2003 05:46 AM in reply to: *Rogerson, Michael
Couldn't a spiral for, say, a parking garage ramp or on/off ramp be > 180
degrees? (or the pedestrian ramps at Giants Stadium). I've often heard
these refered to as "spirals" but most likely because of their 3D shape, not
because they're spirals mathematically. I can't imagine any other time you
would use anything more than a very slight spiral. They are, after all,
just for transitions, and not the curve itself. I've only ever used
circular curves in roadway design, but that's just me. I have used spirals
in rail design, but they definately don't come close to 180 degrees.

Jon Rizzo
Langan Engineering and Environmental Services, Inc.

"Laurie Comerford" wrote in message
> 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
>
>
> "wfb" wrote in message
> > Is this not similar to having a triangle with more than 180 degrees
total
> in
> > the 3 interior angles?
> >
> >
> > "Michael Rogerson" wrote in
> message
> > | 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
> > |
> > |
> > |
> >
> >
>
>
*Comerford, Laurie

# Re:

11-06-2003 06:01 AM in reply to: *Rogerson, Michael
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

"Michael Rogerson" wrote in message
> 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
> > 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
> >
> >
> > "wfb" wrote in message
> > > Is this not similar to having a triangle with more than 180 degrees
> total
> > in
> > > the 3 interior angles?
> > >
> > >
> > > "Michael Rogerson" wrote in
> > message
> > > | 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
> > > |
> > > |
> > > |
> > >
> > >
> >
> >
>
>
*Rogerson, Michael

# Re:

11-06-2003 11:23 PM in reply to: *Rogerson, Michael
For the "spiral" ramp - I think, as you say, more of a "Helix" rather than
any type of 2D spiral. Would make an interesting 2D alignment indeed.

I'm certainly not expecting that anyone needs a spiral greater than 180
degrees, nor I have not ever heard of a request for one, but if there is
anyone out there that can't get something accomplished because of this, I'm
like to hear.

Mike

"Jon Rizzo" wrote in message
> Couldn't a spiral for, say, a parking garage ramp or on/off ramp be > 180
> degrees? (or the pedestrian ramps at Giants Stadium). I've often heard
> these refered to as "spirals" but most likely because of their 3D shape,
not
> because they're spirals mathematically. I can't imagine any other time
you
> would use anything more than a very slight spiral. They are, after all,
> just for transitions, and not the curve itself. I've only ever used
> circular curves in roadway design, but that's just me. I have used
spirals
> in rail design, but they definately don't come close to 180 degrees.
>
> Jon Rizzo
> Langan Engineering and Environmental Services, Inc.
>
>
>
>
> "Laurie Comerford" wrote in message
> > 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
> >
> >
> > "wfb" wrote in message
> > > Is this not similar to having a triangle with more than 180 degrees
> total
> > in
> > > the 3 interior angles?
> > >
> > >
> > > "Michael Rogerson" wrote in
> > message
> > > | 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
> > > |
> > > |
> > > |
> > >
> > >
> >
> >
>
>