I am not a professional railroader, but I watched similar construction here in Fremont CA when the Centerville 2nd main track was installed a number of years ago. I observed the following steps:

1. Top soil removed down about a foot to form a shallow trench where the track would eventually go.
2. Trench filled with base rock (rock crushed to about the size of gravel, but with sharp edges that allow it to compact into a solid base. Used under roads, sidewalks, patios ...)
3. Base rock compacted
4. IIRC, a very thin layer of Balast applied by truck. (Balast is also crushed rock, but with 2-3 inch diameter.)
5. Ties layed out
6. Rail attached.
7. MOW hopper cars used to dump balast up to the rail heads.
8. Tamper-liner used to lift track, align and surface it, and tamp balast under the ties.
9. repeat steps 7 and 8 until adequate balast depth has been achieved.
10. A few more passes of the tamper-liner until the desired surfacing and alighment is acchieved
11. Spruce it up with a balast regulator.
12. Admire track that would make a model railroader envious :-).

I suspect it is cheaper to apply the balast this way than to truck it in, and SMART plans to do the same. It will be interesting to see exactly how it is done in their case.

So, that is how it was done in Fremont and Newark CA during the two upgrades to 2 main track CTC in the late 1990s. After a second project we now have about 7 miles from CP Shinn (near Niles Junction) through Neward Junction to CP Mowry (2 miles South of Newark Junction). All of this is in the SF East Bay area, California, USA.

Drew