Adjacent Track Radii

Back to back streamline points give a spacing (centre line to centreline) of about 51mm, which equates to a rail to rail spacing (between the nearest rails of the pair of tracks) of 34mm. At 4mm/foot (OO) that would be 8.5 feet not 6.
So I'm puzzled at how this "6 foot" spacing is being calculated (Peco's catalogue does this too, so it isn't just you).
Mark Thornton

The "6 foot" is actually the minimum. Look at some of the Great Western main line that was once broad gauge and it's heck of a lot more than 6 feet.
Also remember that it is going to be bigger in OO because of the effect of the narrower track gauge.
The more important things are the dis tance between track centres, and the clearance for any overhang on curves.

"Mark Thornton" wrote
Some of the difference will be accounted for by the underscale gauge of OO-scale track.
John.

With or without a cant under the curves :-) It will give a different answer.
You've got to adjust the track gauge from under-scale OO. The prototype 6 foot spacing is from adjacent rail to adjacent rail. For sidings alongside a mainline, the spacing should be 10ft.
And, if you went to prototype 6ft spacing (suitably increased for the under-gauge OO to 26.3mm), you'd need to be certain that your vehicles stayed within a prototype loading gauge (ie. didn't move left-right on the track within the limits of the back-to-back of the wheels). But, with the pragmatic wheel geometry of OO, there will always be a risk of movement outside the pure-scale loading gauge.
However, remember that Peco track is really to a HO design. So, address the question about spacing in 3.5mm/ft and non UK practise track. It comes out at 10ft or 3m almost exactly. 3m spacing sounds nice and sensible, I wonder what prototype Bern Gauge specifies ?
As to the original question, one needs to know the pivot centres of the coach, then assuming the coach to be rectangular in plan, knowing its overall length, it should be possible to work out the swept arc of the coach for any particular radius. Having calculated a theoretical arc, add a bit for the wheel movement and any other irregularities.
- Nigel

Rob, do not get fixated on ensuring that tracks are exactly 6 feet apart. This is merely railway terminology and a general minimum.
Take a long hard look at any Network Rail infrastructure and you will see that "Real Life" tracks rarely display the 6 foot rule.
Has it gone metric yet?
yoda

The spacing where the footpath crosses my nearest stretch of track is very close to 6 foot (between Hertford and Ware).
Mark Thornton

Yes. It's colloquial. A minimum of "6 feet, something".
They also talk about the 4 feet as the area between the rails.

Actually if you do take such a look you will find that the 6ft spacing is accurately maintained throughout almost all "real life" double tracks. It gives you a centre to centre spacing of 11ft 2in, just a tad under 45mm in 4mm scale. Straight track at these centres will be OK with 00 wheel standards, there's not that much slop in there. With Mk3 coaches and similar long vehicles you are going to need to start widening this out to allow for end and centre throw below about 4ft 6in radius. Keith
Make friends in the hobby. Visit Garratt photos for the big steam lovers.

Yes, track design is metric these days. The "Standard Track Interval" is now given as 1970 mm.
Note this is now defined between gauge faces of the rails, the '6ft' was between outside faces of the rail.
So track centre - centre is 1435+1970 = 3405 In 4mm scale is 3405/76.2 = 44.69 mm. Keith
Make friends in the hobby. Visit Garratt photos for the big steam lovers.

Robert,
One thing you haven't mentioned is the radius of your curves - this will very significantly affect whether you can even lay track at 6 foot spacings. With model curves being significantly tighter than even the tightest of prototype curves, I would suspect that you will need to adopt the Peco spacing, afterall, that is why they have created it the way they have. I once saw a club religiously try to stick to 6 footways on their 3 foot radius curves. Guess who came along and put some Lima MKIII coaches and a 4-6-2 pacific on ? They had to relay all of their track. Graham Plowman

First, ignore protoype spacing on curves -- our model railway curves are very, very sharp compared to the prototype. NMRA (nmra.org) has a set of recommended practices for centre to centre spacing that takes into account both radius and length of rolling stock. Since I don't know what "first radius" etc means (and it's a stupid way of describing a radius, anyhow - why not just use inches or centimetres???), here's a short table adapted from NMRA practice that should provide the data you need.
For rolling stock up to about 50ft long and six-coupled steam locomotives, use the following minimum centre to centre spacing. Interpolate for the missing values. You can measure right rail to right rail, it's easier than finding the centres first.:-)
15" radius: 3" minimum 18" radius: 2-1/2" minimum. 20-24" radius: 2-1/4" minimum 30-36" radius: 2" minimum
BTW, spacing between track and lineside structures is equally critical.
On straight track, the prototype uses different center to centre spacing depending on the use of the track. In yards, the minimum in N. America is 13'6", and it would be a foot or so narrower in the UK. This leaves about 3ft clearance between cars, so a person working in the yard is OK standing between trains on adjacent tracks. I use 2" minimum spacing on straight tracks, which is about 14'6" in HO, and about 12'8" in OO.
On mainlines, the spacing is wider, especially if trains are expected to pass each other at speed. Eg, on the TGV lines, the spacing is 18ft IIRC.
Since UK OO rolling stock is about the same size as US HO rolling stock, the numbers above should work for you. If in doubt, make a test car as follows:
Cut a piece of perspex or similar clear plastic as long and wide as your longest waggon or carriage. Add bolsters and bogies at the proper spacing. (If you add a coupler at the correct height, you can also test coupler height on rolling stock.) You can roll this test car around and see both where the edges come too close to lineside obstructions and parallel tracks etc, and where the rails are in relation to the car.
It's also useful to have a loading gauge test gauge. Cut a piece of 1" thick wood to the outline of your scale's loading gauge, or build it up from pieces of boxboard or other thick cardboard. Make one side a foot or more wider relative to the centre line (which should be marked), and mark this side C. This side is the one you use to test clearances on curves. The other side is marked S, for testing straight track. Leave or add a tab on the bottom (centered on the centre line as marked) just wide enough to set between the rails. Set the gauge on the track and use it to place lineside buildings etc so as to clear the rolling stock.
HTH&GL

"Wolf Kirchmeir" <
Right on Wolf. Agree 100%. What the hell is "First Radius"?
Me. I use 38th radius.
You?
-- Cheers Roger T.
Home of the Great Eastern Railway

Sorry Keith still have to disagree with you on this one.

Graham
When I said 6 foot I mactually meant the Peco spacing, not realizing at the time that the two are not the same. My largest radius will about 55cm and I am hoping to get 2 tracks inside that.
ROB

This is a misunderstanding on my part, when I said '6 feet' I actually meant the spacing that back to back Peco Streamline points provide. My question about the radii that I can get Mk3 coaches round at that spacing, without contact, still holds, though.
ROB

Disagreeing won't alter the facts, why do you suppose its called the 'Standard track interval'? Keith Make friends in the hobby. Visit Garratt photos for the big steam lovers.

55cm (approx 2 foot) radius ? That is _really_ tight. If you are going to put two tracks inside that, the inner track will be down to somewhere around 40-45cm. That really is too tight in my opinion. You definately won't be able to lay a scale 6-foot way with those radii and you will probably even have to widen the Peco spacing to accomodate vehicle overhangs.
Graham

Phil: Well, I don't know how much space YOU have available, but unless one wants to build a straight line track and spend all ones time with fiddle yards (as some exhibition layouts do) then in a British home there is little option than to use 2ft (600mm) radius! Especially when viewed from INSIDE the circle this is quite acceptable. It is also about '3 radii' more than 'uk geometry' (as set by Triang Hornby Series 4 track/system 6 years ago), and much more than the 250mm radius included in Roco starter sets with an ICE2 train! I will be having 1 siding on about 17-18inch radius so that it looks tighter, and I will also be using many Fleischmann points (standard brass radii) for my main sidings. This provides a contrast to the 600mm minimimum radius I try to use elsewhere. But how do I then best represent 'Barnstaple Bridge' - a tight curve with check rails over the River Taw where the original does an S curve from Barnstaple Junction to the Town station (1 curve over the river)..if not on the minimum radius I can use for all stock? I am split between 18inch with a straight section between reverse curves, and 600mm with no gap between the reverses...or since its Beechingless Barnstaple....building a new bridge that is straighter! 8-(

Why do you persist in this ridiculous nonsense.
are you a rivet counter?