This railroad had nothing to do with COVID relief, but you are in your rights to think so, and the thought of a underground high speed rail for the Silicon Valley folks to use does sound cool.
My fear is that this money (that could actually have been used for COVID relief) will be spent trying to build this cool underground rail but there will be problems, cost overruns etc. and the railroad will never be finished.
This isn't really how spending of this type works. The economic stimulus bills have had several independent goals. One is to provide emergency funding to meet healthcare costs and vaccine distribution expenses so that the pandemic can end. Ending the pandemic is the first, and absolutely necessary, step towards getting the economy to recover, but it isn't enough, by itself. The economy has undergone a historically large shock. The way you address the economic impacts of Covid is through fiscal and monetary stimulus.
For economic recessions of this sort, fiscal stimulus is generally the more effective policy option. This is something that both the Fed chairman and treasury secretary have discussed in public comments recently, and its something that most professional economists agree on. Among the options for fiscal policy, infrastructure spending (roads, trains, renewable energy, airports, etc.) historically have high returns, both in terms of their immediate effects on returning the economy to its pre-recession levels and on providing longterm benefits.
Not to discount what you're saying, because it's always reasonable to be concerned about cost overruns and the like, but I would caution you not to miss the benefits of infrastructure spending (and fiscal policy in general) because of these things. Yes, keeping projects on time and under budget is important, but what is more important is stimulating the economy and getting people back to work. And that has everything to do with Covid.