It's only hard because of the destructive and segregationist DECADES of policy of expanding the suburbia.

I assure you, in most places outside of the US, public transport does go to last mile pretty well.

Well, i live here in Belgium ( good public transport/very wide coverage). The hard thing about public transport is that you have to find out where to go / how, if you are suddenly changing plans in a "not-known" area.

Not only that, it takes significantly longer than going by car. I think Elon Musk brings the best of both worlds by reducing travel time and avoiding busy roads/traffic jams ( no need to build it on the countryside) and if you want. You can return by night. Also, in Belgium, all our roads have severe traffic jams. The tunnels could reduce traffic jams on normal roads. Records break year after year with no solution ahead. ( and yeah, our governement invests a lot in public transport. It isn't profitable now and it will never be profitable -- heavily subsidised)

No public transit is affordable at night over a long distance. Almost everything happens by daytime.

I'm not saying public transport is bad, but it's not cost-effective if you want it everywhere / everytime.

This could really be the solution, it's genius. The cost of the tunnels would be paid back in a short time, only because roads are less jammed.

We already tried fast roads that avoid traffic in America in the form of elevated expressways that criss-cross the city core. They are an absolute eyesore and end up creating more traffic themselves due to induced demand. I think the real solution is a good, high-frequency public transport grid combined with an autonomous taxi or micro-transit system.

There's an easy way to get rid of suburbia:

Stop forced integration in cities.

As soon as you eliminate housing projects, housing wavers, rent control, etc., and allow the market to deal with housing naturally, suburbs become obsolete.

However, so long as governments provide cheap or free housing to criminals, dropouts, homeless, and those who in an earlier age we would have sent to sanitariums and rest homes, people are going to flee to safer areas; thus, suburbs.

I suppose you could also keep existing housing policies in place, but step the police presence WAY, WAY up, and get significantly harsher on criminals committing even minor offenses. Rudy Giuliani did this in NYC, and New York was able to be wildly diverse, yet also very low crime and a nice place to live. But I'm not sure the will is there in L.A. for a "tough on crime" approach.

The solution to this "last mile problem" is to improve the public transit network and urban design such that the last mile is a pleasant walk or bike ride on public bike share system integrated with the public transit system.

Might work great in the summer, but growing up in Toronto, you really appreciate having that bus stop next to your house in February