I guess we should consider ourselves lucky that the last "gap" in 58, east of Boron, made it through the process and into construction, that actually carries the trucks from the Central Valley to "points east." The HDC would have been oriented more at the trucks between the transload centers of the Inland Empire and I-5, taking them out of the Basin. That would be a Good Thing from a local air quality standpoint, but the "induced trips" people would prefer that the trucks trundle along the 210 and the 10 and the 60 stuck in traffic I guess, since they would argue that all those trips would stay there and any trucks using the HDC appear out of the ether.

Based on my recent travels to SoCal (which uses the desert and the 15 to enter the IE, rather than fighting my way through LA), I'd guess that there's precious little remaining capacity for trucks on 15, regardless of what happens with the HDC. Almost always a total-stop traffic jam ENTERING the LA Basin (not just leaving it heading for High Desert suburbs and Las Vegas), mostly trucks in the 3 (of 4 or 5 depending on where on the grade) right lanes, heading DOWN the hill southbound. And even on Sunday morning north(east)bound, the right 3 (of 5) lanes are bumper-bumper trucks (luckily, the other lanes are clear enough at that time to allow some passing). Looking at it from a broader perspective, I would discount that "induced travel" argument considerably - a shortcut to I-5 might be desirable, but isn't of much use if you can't get to (or from) it.

As for the trains: without the freeway, I don't think HDC environmental work will be completed by Metro or Caltrans. The data developed might be useful for Virgin to complete something or the train, though.