[supernova87a]

Tunneling in the US is massively expensive, which is a huge problem for infrastructure projects. There have been some previous posts on exactly this topic ("why do projects in the US cost so much?").

And we are out of money / unwilling to pay for such projects. Australia is still relatively swimming in its natural resource boom and has funds to do that. And political willingness to invest in public transportation that's clean and efficient.

In California, public transport seems to be relegated to the status of a homeless mobility system / shelter, that most people reluctantly take and have to wonder why it's so badly operated. I don't think the idea will get far to tunnel under the rest of the peninsula. We can't even sort out the remaining 1 mile of Caltrain that was planned to connect to downtown SF and the Transbay center.

Aside from that, I believe there's a groundwater level problem under most of the places where such a line would go? I'm not an expert on that though.

[skissane]

> And we are out of money / unwilling to pay for such projects. Australia is still relatively swimming in its natural resource boom and has funds to do that.

On a per capita basis, the US is richer than Australia. According to 2019 IMF estimates, US's nominal GDP per capita is US$65,111 (ranked 7th), Australia's nominal GDP per capita is only US$53,825 (ranked 10th) [1]. Similarly, the US's PPP GDP per capita (2020 IMF estimates) is US$67,426 (ranked 10th), while Australia's is only US$54,799 (ranked 19th) [2].

The US is a richer country than Australia in both relative (per capita GDP) and absolute (overall GDP) terms (and both nominally and at PPP). If Australia can afford tunnels, why can't a richer country like the US afford them too? (Especially in the Bay Area Peninsula, which is one of the wealthiest areas in the whole of the US.)

[1] https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nomi...

[2] https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(PPP)...

[supernova87a]

But the important other factor is government debt.

Australia's national debt is less than 1/2 of the US's in terms of % of GDP. (US has basically 100% of its annual GDP in debt). Australia has a lot more room to consider big projects as a result.

[skissane]

I think a lot of people have an excessive fear of government debt, especially given how low interest rates are nowadays. Countries (including the US) should be borrowing more to stimulate their COVID-afflicted economies.

Putting that aside, a common trick used in countries like Australia and the UK is to keep big projects off the government's balance sheet through public-private partnerships – private corporations do most of the borrowing, not the government, and end up owning the infrastructure (often under some deal where it reverts to government ownership in 50 or 100 years time). But I get the impression that approach is far less common in the US. (Despite the fact that it is the more capitalist/free-market approach – allow private investors to own public infrastructure – and the US is generally thought of as a more capitalist/free-market country than the UK or Australia are.)

Public-private partnerships are often criticised as being inferior to government borrowing, due to higher private sector borrowing costs, and I agree with that criticism. But, even though I think it is best to build with government borrowing, if one has a government debt allergy preventing that, then building with private borrowing seems better than not building at all.