I have never used easements on a layout. Let’s assume I have a peninsula and want to add a half circle of track (30-inch radius). The appropriate easement is 1/2 inch per side. Does this mean the net radium of the half circle is now reduced to 29"?
Do you have room for the extra half inch on the outside of each end if the curve. That way you can keep your curve at 30" radius and then ease out a half inch on each end of the curve.
Wish I could say yes… The actual peninsula is 60-inches wide and my actual planned radius is 27 inches, providing a minimum of 3-inch buffer to the layout edge. I’m just trying to understand the geometry.
The radius would be 29 1/2 inch since each 1/2 inch is out of the 30 on its side.
Alternatively you could add it to the outside and your over all width for a half circle would be 61 inches - 30 1/2 inch per side.
Or you could split it so that you reduce your radius to 29 3/4 and widen your half circle by 1/4 inch on each side for a half circle width of 60 1/2 inches.
Paul
Hi IDRick,
You are correct. What you have to decide is whether or not an easement will make any difference to the appearance of your trains as they go through the curve. IMHO, the difference is related to the speed at which your trains go through the curve. If you are running slowly then the lack of an easement won’t be as obvious, but if you are running at higher speeds then the scene will look better with the easement. Your trains won’t be suddenly ‘launched’ into the curve like an O scale toy train on tight radii.
The difference will be subtle, but I much prefer the easement option.
Dave
In the model world it is perfectly acceptable to layout easements by eye. I personally used sectional track on my layout. Using one piece of the next larger radius at each end of a curve gives nearly the same performance, in the model world, as if one actually followed the (simplified) easement geometry in the layout design books, or else “curved by eye” the transition. Personally, if I had a 30" radius curve, I am not sure that I would bother trying to do an easement, because at that radius, unless running high speed passenger equipment, there isn’t much of a “sway” affect as what happens in real life when there isn’t an easement. I used Kato 26.375" (converted U.S.) radius, with 28.75" radius sections at each end of a curve on my mainline, to provide the “easement effect”.
Later when I enlarged some curves to 30" or 32" radius I didn’t worry about easements or rather just curved them by eye. The long 89’ or 92’ freight cars do just fine for me…I do recommend laying one out and then, if possible, testing the equipment to see how it looks, before finally gluing or nailing the trackwork down in place.
John
One of the great things about Atlas flex track is that it naturally forms beautiful easements if you allow it to as opposed to the much stiffer ME track which must be meticulously bent to form easements.
no. the curve widens to 30.5", becoming an ellipse.
Echo’s approx what I posted ealier.
The diagram is basically what John Armstrongs books illustrated; a must read IMO.
Yet for some reason there are those who prefer the stiff “flex” track. As you noted Doug, Atlas forms it’s own easements nicely.
I don’t understand the need for easements either, depending on the radius. Of course I run all of my trains at 25 mph or less. But our layouts all have terribly sharp curves compared to the prototype, so I’m not sure of what real gain there is entering a curve with a 1 inch smaller radius than the prevaling radius. Speed exacerbates the sway, not the nominal difference in radius. JMO.
Seems to me to really gain the visual effect, easements are going to have to be pretty long and space consuming.
I think having easements makes a huge improvement in the visual effect of running model trains specifically because the curve radius is so much smaller than the ‘real’ world.
I think about driving a car down the road at 50 MPH and going into a turn. Unless you’re a F1 driver, as you slowly turn the wheel to start the turn you have created an easement which greatly smooths out the transition of the curve. However if you immediately turn the steering wheel from 12 o’clock to 9 o’clock (which is what a train does when entering a curve with no easement) everyone leans and slides to the right.
I don’t see any downside to using easements other than the slightly more space required.
Yeah but… I lay my track on homasote or cork roadbed, which is laid on plywood cookies. By the time the track goes down, I’ve already committed to the center line.
In TPFRO, Armstrong explains that an eased curve of a tighter radius performs better that an un-eased curve of a larger radius. So… if you need to reduce your radius by 1/2" to fit in easements, it’s worth it.
Because of what John Armstrong colorfully called “the coefficient of lurch” in Track Planning for Realistic Operation, the straight-to-curve transition is often the critical point for performance and reliability of specific railcars or coupled combinations. (Which is intuitive.)
In my experience, an adequate easement may allow a piece of equipment to negotiate a tighter radius than an un-eased curve. For track plans where a couple of inches of reduced radius makes a difference whether a turnback curve will fit in the room or not, it matters a lot. (And these situations are common.)
Testing has been started to measure the actual benefit of a “bent stick” spiral easement in terms of radius. Quick rough tests suggest that it might be the equivalent of a couple of inches of radius for some classes of HO curves. But more work is to be done to characterize the benefit conclusively.
Byron
Thanks guys, you’re always very helpful! 
I will be running a switching layout at slow speeds with 4 axle diesels and longest car is 57 ft (scale equivalent). Time period is the early 90’s. I am using atlas flex track so will be putting in the easements.
Oops, I meant entering a curve with a 1 inch LARGER radius than the prevailing radius.
I understand the principal conceptually. But how much space does it take to do easements properly? There is always a lurch with our tight radius (compared to prototype) layouts, unless we take gobs of space to go from tangent to the prevailing radius. The example given was starting off with an easement of about 30 inches to a prevailing radius of 29 inches to take up the same amount of space. I di
Me neither. After I had devoured my copy of John Armstrongs book in the mid to late 1980’s, it was a no-brainer to include easement in my first 16x19 layout and I’ve been doing it every since. The slightly more space of about a half inch isn’t so space consuming as some suggest.
Here is the thing. All you have to do is allow for that half inch when designing the sub-roadbed and draw in the centerlines. Cork is laid similar to the flex track, you
My point was that since you had to plan the centerline before laying the track, the natural tendency of Atlas flex to create an easement provided no value.
Well, its still a brainer for me. I guess its a matter of what the book was calling an easement and what Armstrong was looking to solve. I doubt if he was talking about a prototype easement scaled down to its modeled length. I think Armstrong is talking about avoiding violent lurch to help model trains or toy trains (back in the day) operate at high speeds. Which might be the goal for many.
That’s not a spiral easement. I’ve observed a significant difference when a real easement is used.
A “bent-stick” easement of 1-to-1½ car length seems to help a lot and doesn’t take up much room*. This approximates a true mathematical spiral easement, the complexity of which doesn’t seem to add much benefit in the model.
Prototype easements are often used to transition to-and-from super-elevation, so they need to be longer.
- But there’s no free lunch, there is some tangent (straight) track lost to the easements. The trade-off is often worth it.
Byron
That’s exactly what a (spiral) easement is? And that’s how I have (tried) to lay my track. The objective is no ‘lurching’.