OK, this isn't to start another "crunchy wheat, nicely sweet" discussion about whose track has more selection, potential or whatever.
This is merely to show that these two track systems can be joined and work together with a little modification.
Rail height for both the Lionel & SHS track is .133”
The base of the rail for both is .104” wide
The web of the rail is the only measurable difference. Lionel is .025”, SHS is .023”.
For all practical purposes, the rail is identical.
But, the locking systems aren't even close. To join these two track systems together, something's gotta give...
The easiest is to remove the socket on the FasTrack and create an opening for SHS plug to fit:
With several cuts with a razor saw and scoring with an X-acto knife, an opening a half inch wide will allow the enough clearance for the SHS plug to pass through, allowing the sections to be joined.
Then, all that's needed is to now is to a little clean up and join the two sections together and you're done!
Obviously, the locking feature of these two track systems is gone at this point, but either a metal clip could be formed or a hole could be drilled on the ends for a small screw and nut to hold the track together. For a permanent transition piece, an ABS compatible glue could be used.