Yeah it happens a lot here as well. It goes into contractors pocket who dig/drill/build -> stop -> dig/drill/build -> stop and get their $$ on partially completed work and milk the system for all it will give them. Quite often they are friends/relatives of the politicians.
Here in the EU, we usually consider Italy and Spain somewhat more corrupt than the Western average, but high-speed rail in both countries got built reliably and without major delays.
Even though both peninsulas are mountainous, by no means an easy terrain.
California contracting in particular is built not of penurious individual corruption, but of systemic corruption. The lowest bid must win, and nobody has the political capital to establish a bidding system that works, so dramatic systematic underbidding + cost overruns is the rule, and is expected by all parties except the naive public.
Couple that with the kind of "Build nothing if any single problem can be detacted", 'Cheems mindset' failures of liberalism, and high-pressure demands from a federal government whose legislators are eager to sabotage projects outside of purple states.
Here in the UK all Gov tenders are on a combination of price and quality - typically 40-60% quality. If you want a long term relationship as a Gov supplier, you need to demonstrate quality and bid the pricing fairly, without chronic underpinning.
Idk about Canada, but what you usually see in the UK is that tens of millions of pounds get spend before a single brick is laid.
Money disappears into consultations, reviews, studies and reports of dubious value, the paperwork keeps piling up and it takes years before the public sees anything tangible, if the project ever gets built at all.
Someone somewhere is getting very rich off this, but it ain't the taxpayer.
All those billions of dollars are going to someone's pockets. There's a lot of money to be made from inefficient infrastructure projects.