I don't think anyone really likes living near a highway. They're loud. (VRRRROOOOOOOOOSSSHHH!!) They're grey. They increase the amount of traffic near you. And when there's a traffic snarlup..... HONKHONKHONKHONKHONK, and then it promptly spills over to the nearby streets, because people get impatient. I'm sure the city doesn't like the loss of so much land either. So much land that could, I don't know, be a business district.
I'm imagining a layered highway. On the top layer, a two lane road with a business district on either side. Quiet. Calm. Peaceful. 35 MPH speed limit. And occasional lanes down to a lower layer. This one has no stop signs or traffic lights, and the speed limit is 55 MPH. It's enclosed, which reduces the sound the cars make, with paintings along the side showing what the next exit leads to. The exits are special lanes that go back up to the surface street. And in the middle, there's an occasional lane down one layer more.
The lowest level has speed limits of 120MPH (or higher). It's meant for the really long hauls, Interstate or further. Fans on the ceiling drop air resistance by a significant amount. Your massive rocketing speed remains unnoticed at the surface, as you are quite some way down. Exits lead back to the main freeway level every so many miles.
Ideally, this would use the earth as a sound absorber. If you lived near this freeway, you might not notice, even though the lowest level's outer lanes ran directly under your house. You would just notice that there were shops nearby, and when you needed to go in the freeway's direction, you could get going at a fast or ludicrous pace within a very short amount of time.
I have three concerns to work out. One is exhaust. If I don't vent it somehow, it will build up to lethal levels in the lowest tunnel. Another is water management. If this gets lower than the local water table, all hell breaks lose engineering wise. The last is breakdowns. If you run out of gas or your engine fails at the lowest level, then what?