To solve Sydney's road congestion nightmares, NSW government is spending, or I should say, wasting, billions of dollars building a "parallel road" (a $2.5 billion, 31 km duplication of the Great Western Highway between Lithgow and Katoomb)  which will almost certainly increase the air pollution, damage the precious bushland and will destroys the houses of many people.

As ever, NSW government's tradition of underestimating costs and misplacing funds, they are deaf to calls for a much more straightforward solution that would not damage the bushland, would not touch people's houses (with the proposed locations of portals) and would eliminate much of the pollution that would be created by NSW's "parallel road" "solution".

The solution that the NSW government would not really consider is a tunnel through the Blue Mountains.

The tunnel idea was first floated by Jeremy Buckingham, an independent MP for NSW. On January 16th, he asked Elon Musk, via Twitter, how much would such a tunnel cost under Blue Mountains. The Boring Company boss would come back with a prompt reply on the same day (albeit on US times):

https://twitter.com/elonmusk/status/1085463656345694208

Elon Musk is known to have built things initiated by his Twitter exchanges. One example is a battery plant he build in Australia.

But Elon Musk's cost quote for 50km tunnel through the Blue Mountains "About $15M/km for a two way high speed transit, so probably around $750M plus maybe $50M/station" has been dismissed by some as "Alice in Wonderland" talk.  I think one thing people overlook is that, Elon Musk's tunnel is not a road tunnel where people drive through with their vehicles. Wheras, Musk's tunnel would normally be the one where you could put your vehicle on a sled and the sled goes through the tunnel. Probably such a tunnel will not have any ventilation or so.

Now Buchingham's tunnel idea is again in the news with Blue Mountains' Labor mayor Mark Greenhill opposing the highway. It might help the chances for a tunnel.

https://www.smh.com.au/national/nsw/irreversible-damage-is-a-tunnel-under-the-blue-mountains-the-solution-to-traffic-woes-20200821-p55o5s.html