Here are a few things to consider:
- If the grade only runs in between switches and the switches are all at zero (benchtop) height, then grades would be close to 6%.
- If the grade begins upward on each side of the underpass and switches are within an existing grade, the grades could be built closer to 3.5%. However, SCARM doesn't permit switches to be inclined within an established grade, it requires them to be level.
- Vertical easements at the beginnings and ends of grades help the train more smoothly transition from one plane to the next , versus an abrupt change in vertical angle. Abrupt vertical angle changes can cause binding, stalling, wheel spin, and/or derailment. So even with enough hypothetical space in SCARM for say a 3.5% grade, additional linear space should be allowed to transition between grades. How much length to be allowed depends on the length and type of trains/locomotives planned to be run on the layout.
- With the FasTrack O-72 Wye, SCARM doesn't automatically add the 1-3/8" half-roadbed fitter pieces that come attached new in the box. These pieces allow the Wye switch to be fitted into a track plan without the need to cut adjacent track. Here's what it looks like without the fitter pieces,
In the first image below, the red track's grade begins at the lower right switch. This would be a 5.9% grade without vertical easements. Note: to reduce the grade a bit and allow inclusion of the 1-3/8" fitter pieces with the Wye, I've swapped out the O-72 curves with O-60.
In the second image, the grades are closer your 3.5% target and begin their incline on either side of the underpass. Switches are only removed so that the grade can be shown continuously within SCARM. These also don't yet have vertical easements.
For your consideration, the SCARM file with these suggestions is also attached.
