We've written at length on the challenges faced by California's high-speed choo-choos, primarily on the fiscal end of things where Governor Brown has purposely and cynically de-scoped the project to get the price tag from the $100 billion range to merely $68 billion (as advertised at time of inception $33 - 40 Bil) by carving out the electrification and the whole actual choo-choos parts.
As engineers, we've touched on, in general terms, the logistics and civil engineering challenges also posed by employing 19th century technology and expecting 21st century results. The biggest physical hurdle the choo-choo project will face and what jumped out at us as obvious when we first heard about the project was how was the trans-peninsular range of the Tehachapi Mountains going to be negotiated.
The video below is a a great illustration of a Southern Pacific freight train slowly making its way around the Tehachapi Loop between L.A. and Bakersfield at a speed of 10-15 mph, essentially traveling a mile or so and making up absolutely zero ground over land.
You see, a steel on steel mode of transportation is terribly inefficient on grades and, in fact, as the Loop makes abundantly clear, the rule of thumb for gradients is to not exceed 1% elevation change. Would high-speed train technology make anything different. Possibly but from strictly an intuitive standpoint, probably not much. (Traveling at 40-50 mph would be a quantum improvement over the freight speeds but still a snail's pace by high-speed standards.)
$68 Billion in and we have before us yet one engineering/logistics challenge out of possibly many more no one really thought through before this project was put on the ballot back in 2008.
H/T: Leslie at Temple of Mut