Away from the layout I could waste obscene amounts of time on trivial questions like the size of turnouts. As they say: “Evidence Jim. You got any in there?”
This is a photo of two paper templates from Fast Track’s library of On30 turnouts. Measured from the points of one to the points of the other there’s less than half an inch of difference in length. An unglamorous, so unphotographed, second measure is the place where cars on a trailing siding would foul and the result is about the same small amount.
The culture of our popular design tool kit advocates using the largest turnouts we can and I agree. I’d rather have fewer turnouts if their geometry is more fluid and natural looking too. However that same design toolkit has a habit if perpetuating “I used number fours in the yard to save space.” but we really didn’t save that much space and that decision, no matter what scale, gauge, or standards you use, does affect what trains you can run or how reliably they will navigate those same turnouts.
When I’m working in a yard I tend to drill longer cuts of cars at once so am typically shoving back a cut through a maze of number fours and hoping things work out. That train is usually short cars so their individual length is fine but their accumulated character, as a train, changes things. So, this isn’t about autoracks or passenger cars either.
Categories: model railway design, Trackwork and Handlaid Track
Prince Street 
The frog angle affects how far you have to go to get clearance between two tracks. Getting to the frog is just the start of the “journey”. :-)
I agree but, what’s interesting is how in this one move, 4 to 5, or 5 to 6, that fouling distance isn’t bad either. I’ll reshoot the photo I took showing cars on adjacent tracks—that reverse curve at a passing siding, that should create the most swing and closest foul, and it’s still a short measure.
Rebuilding the test to measure the distances trailing turnouts for the location of a fouling point.
In both cases I laid up a crossover of two turnouts, same hand, back to back. A true crossover has different geometry from what I’ve done but…what I need is to recreate a reverse curve like you’d see at the start of a passing loop.
Bachmann’s On30 rolling stock is various widths and lengths. For the sake of this I’ve used: a Bachmann On30 baggage car (1-7/8” wide) as the car overhanging on the curve; a Bachmann On30 twin hopper (2” wide) as the car on the straight route. These cars are more like the sizes of three foot gauge stock instead of narrower, albeit often same length, two foot gauge cars.
Distance measured to the fouling point is measured from the tip of the frog (“crossing nose”) to the place where both car’s bodies intersect.
I’m using 2-1/4” track centres in this test. This is narrower than NMRA or the modular clubs use but what I used on my layout and it worked fine.
On the #6 crossover this point is the 7-1/2” between the crossing nose and where the cars foul. On the #5 crossover this distance is 7”.
Since we’re working with geometry here, relationship of the sides of a triangle, I would expect that we’d see predictable (same) comparison distances for a smaller turnout, such as #4 compared to #5, or larger #6 compared to #7.
Since the track centres stay constant the variable here is car lengths in the siding. Tip of frog points to tip of the crossing nose is 1/2” and the fouling point distance is 1/2” so using a #6 turnout costs about an inch in car lengths compared to a #5.
I enjoy this kind of exploration. Even more so because it feels like what we’d do professionally when we relate anecdotal evidence to quantitative data and our analysis is to explore and objective place that gathers somewhere between those two points on a scale.
Chris, you can get away with a longer turnout in a shorter space if you introduce a short curve beyond the frog. Essentially it’s a #6 turnout cocked a few additional degrees to the equivalent angle of a #5. At the top of the ladder there’s a short curve of a few degrees to set the angle of the ladder turnouts and as each track leaves the lead, a corresponding curve to negate the added angle.
I’ve used this method on my Midland Railway in a small yard. You can read about it, here.
https://midlandrailwayblog.wordpress.com/2016/05/25/turnouts/
That was just an absolute joy to read for steps you worked through on their own. It’s one thing to see work that’s done that is attractive but a completely new and wonderful level when the book, behind the work, is opened to reveal such thinking. I adore this stuff.
Chris
I agree and that’s a great idea too. In a bunch of plans I’ve redrawn in CAD I’ve also used a variety of asymmetrical wyes to gain larger number frogs in smaller spaces and, given my preference for lacey, wandering, plans, this works for me as well.
Your mention of laddering turnouts reminds me of all those great compound turnout designs that we just don’t build enough and sometimes it’s tempting to indulge in–for the sake of building turnouts.
Chris