I was driving around my hometown of Columbus, Ohio and started noticing that a lot of our interstate mileage is not at grade but rather trenched or elevated (be it either earth or bridges). A lot if times it is only trenched a few feet deep but I'm counting that. I think it's interesting since the city is quite flat to start with. There are indeed at-grade sections such as I-270 on the west side north of I-70 and I-70 between James Rd. and Hamilton Rd. -- but just not that many considering the city's topography.
Off the top of my head, a city I think of having a lot of at-grade interstate is Orlando. Or at least until very recent upgrades.