3
3: Branchline track uses less rock and is rated for lower
speeds.
There are a couple of key dimensions in the main line profile
(2). Note that the ballast should be about 2” lower than the
top of the cross ties, not level with them. The diagram shows
12” of ballast under the ties, and a uniform 6” of sub-ballast
below that. The sides are sloped at 3:1, and the roadbed
extends for a foot on either side of the ties before it slopes off.
Not too many modelers are going to work to those exact
dimensions, but it gives you the proportions of how main line
track would have looked at the time of this 1979 diagram.
A branch line profile (3) is a little different. There is only 8” of
ballast under the ties, and only 6” beyond the end of the ties.
The edge slope is the same, 3:1, and there is still a 2” layer of
larger crushed rock under the bed of ballast. For a point of
comparison, the mainline spec called for 4185 cubic yards of
