If you can get natural light in people could live under the mound. Then you can have a city that looks like a park! People could quickly walk or cycle to where they need to go. Cars stay in tunnels.
You might also might be interested to know that Millennium Park is actually a massive rooftop garden covering a train station and parking garage which connects to a lot of these streets.
I’d also add that street level was raised off of the ground in the 1850’s, but that was just to help with drainage afaik.