The Big Dig was a little more complicated than this.
It contained one new bridge on I93. One completely new tunnel to the airport under Boston harbor. Then they buried the interchange between I95 and I90 under ground. Another 1.5 miles north to south. Another 2 miles east to west. Plus the interchanges to the existing tunnels going and coming from the airport. With all the on and off ramps. Under a city that was 300 years old with a lot of it built on land fill.
It was originally proposed at $2.6 Billion. Reagan VETOED it. Tip O’neil had the votes to override his veto. It ended up costing $14 BILLION.
It is a huge improvement to downtown Boston.
And when it opened I recall sections of metal plates on its ceiling fallng down, right?