Here in Dallas our Central Expressway (Highway 75) is sunken just north of downtown. Personally, I think that it's much more asthetically pleasing, but it does cut down on noise pollution drastically. It cuts through the most expensive part of town and there are actually small residential homes sitting right next to (on top off) the highway. It's quite interesting. It also compacts space (at least in real life) by allowing the access roads to be built right next to the highway and even above the highway.
For the best satelite view, pull up Mockingbird and 75, Dallas, Tx in GoogleEarth.
