"drawing to the width of the ties or the width of the rails?"

I prefer track plan drawings with  two lines the width of the rails so the turnout frogs and points have the proper locations. Also makes it easier to determine clearance points or problems. If you find you need the roadbed outlines for construction you can add it with a different color, or layer later. .DaveB

I used 2" also

Assuming HO scale since you said 2". FWIW Midwest HO cork roadbed is 1-3/4" wide. I used 2" in XTrkCAD because it allowed me to easily spot mistakes in the printed plan. If the 2" marks overlapped anywhere then the minimum track-to-track spacing wasn't maintained. From a construction perspective it really doesn't matter what the outline spacing is since you lay roadbed using the track center mark. 

XTrkCAD prints the outlines, track center, and rails on the paper. Plenty of guides to use.

I should have specified HO scale

And to be clear I'm using AutoCad not XTrkCAD or other program specifically for rail design. I am learning AutoCAD for work as well as pleasure so even though it's not as ideal for track design the skills carry over to other disciplines. 

AutoCad

AutoCad has the necessary functionality to create multiple offset lines each time you draw a line. You could set those to be rail spacing , tie width, roadbed outer edge, and finally minimum track spacing thus replicating XTrkCAD functions.

I used....

the width of the railheads.

I'm using CATIA

I use CATIA for work and occasionally have time to work on my future Free Mo modules.  I can't offer AutoCAD advice directly, but I draw the centerlines first, then offset that centerline by 0.875" (on both sides...0.875"x2 =1.75").  Then i make the centerlines Construction Elements (if I don't do this, I will get errors during the next step).  I then close the roadbed profile by drawing lines at the ends of the offset centerlines and Pad that profile 0.1875" (it might be called Extrude in AutCAD).  To mimic the profile of cork roadbed, I chamfer the edges 0.1875x 45°.  I don't draw the ties or rails, it takes too much time for something that doesn't matter at this stage of design.  Once my virtual plan is 'done', I get all the track components and lay them out, then lay cork where the track components are, not where the centerlines from the CAD tells me to put them.  There might be minor shifting of turnouts but no big deal (like 0.25"-0.50" or so); I don't use any super complex turnout arrangements, the most complex trackwork was 3 turnouts close together...and I got everything to fit just fine.

Use CAD to make an accurate 'sketch', not an exact plan.  Don't expect to print the plan out and lay track directly on top of the centerlines.  It can be done, but I've found it's not necessary.  I take several weeks of tweaking the plan, imagining how trains will run and making adjustments to siding length/location/etc.  I like looking at the plan in CAD, I can spin it around, zoom in, look at it more from track level to see how everything looks before starting construction.  Although CAD is overkill for track planning, I use it because it's available to me and I've gotten pretty good at it over the years.  I started to model a Micro Engineering turnout in 3D, but deemed it was unnecessary...and time consuming.  When the level of detail goes up, it's more like building a virtual railroad, like Train Simulator or similar program...and that could turn into a whole separate hobby.

A Scale layout drawing with Autocad

I use Autocad and draw a rail using architectural scale and then offset the rail head at 3/4 inch to represent the appropriate distance for the gague (HO). I also draw a series of turnouts at this scale. I can then just select and copy one  into place. Gives me quite an accurate drawing. Line, copy,mirror,offset,trim,move and rotate do most tasks.

Doug

...

You'll be best served to simply draw the centerline, if you;re not using a program with everythgin already loaded [like xtrakCAD] 

Centerline only

Benny,

How do you figure? Doesn't not showing rail or roadbed edges make it harder to view the overall plan with how the track relates to station platforms and other structures? Or the module edge? Sure without using xtrakCAD or Templot or doing a lot of geometry myself I won't have the precise profiles of the turnouts. But turnouts are pre-manufactured in my case. What isn't pre-made is the plywood roadbed I plan to cut to shape. Just for studying it's appearance here is the module drawn with 1.5" wide "rails" or "roadbed". It's more to study the interplay between all elements than to come up with an exact track plan.

Base it on Clearances

I'm with Matt (Rustman) and Alan (LKandO); add lines beyound the railhead width to spot clearence issues between structures/scenery and rolling stock, between roadbeds, and clearences between adjacent trains.

...

No, because as CT Doc says, you then base everything off clearances.  I suppose some people have to See more than others, but in my case, I already know that singe line encompasses rail, ties and ballast, which is then on top of the roadbed.  The big important matters are the 2" separation between the two centerlines for parallel straight track, or the one inch distance from that centerline to where you must have overall vertical clearance.  Of course, there is then the profile of everything below the level of the rails,but I don't stress too much about this, I just build it.

I draw centerlines but...

I have duplicate layers underneath I can use to represent track, ties, ballast, and clearances, all by varying the line weight of objects on each layer.

 I suppose some people have

That's me. I know what you are talking about though. My father used to build canvas boat covers. He could draw a square on a piece of paper, write down a dozen numbers and turn canvas into a three dimensional object. All I could see was a square with lots of extra numbers. 

Centerlines

  If I am working in Draftsight, I just draw centerlines, as all the other dimensions can be offset as lines on other layers from there.  Generally I only use this drawing type CAD program to draw out turnout templates for handlaying.  For all the layout planning work, XTrak CAD is the better tool (less to draw manually, more complete library of pieces, allows animation of trains to check operation).

  If I had a specific building I wanted to check clearances on, or design around, I would draw it up in Draftsight (AutoCAd, etc) and figure out how to add it to the XTrakCAd building library.  But mostly that is just because I am cheap and my licensed AutoCAD is a DOS based version ... :D

Toni

ACAD

Well, when I was in high school, I was into sectional track, and made blocks for everything. With the functionality of ACAD nowadays, you can design as much detail into the block as you want. So on one layer, you can show sub-roadbed, on a second layer you can show the track itself, etc. So the queston is, what size sub-roadbed do you want to use? Using layers, you could then print by layers and have a set for laying out the roadbed, followed by a track set of prints.

As I will be using Unitrack in the future, I have begun modeling the track in SolidWorks. Same principle, just with 3D. If you have questions on ACAD, feel free to contact me off line.

AutoCad Blocks

 Rustman,

  I designed my HO railroad using AutoCad MEP 2013.  I do not illustrate the roadbed on my drawings but do illustrate the track center lines and the rails. I offset the centerline .3515" in each direction and then put the new lines on the proper layer titled RAIL. I only showed the rails for reasons of aesthetics

  I have created several blocks that you may find of use: #s 5, 6, 8, and 10 turnouts, a double crossover utilizing #8 turnouts with a 2.5" track center spacing, etc..  I am more than happy to share, just PM me.

Todd

So...

Since I have not had a chance to model all of the Kato track in SolidWorks, I thought I would try playing with XtrkCAD while SW was running in the background fixing a model. Turns out XtrkCAD will not only export to DXF, but the track comes out with detail. I did notice a minor discrepancy between the width I received from Kato and what it exports, but it might help out some.