A former student sends along this:

First, I got a hold of an interesting document many years ago from the City of Minneapolis on Capping Freeways. Can't find it any more though, they may have a copy sitting around.

Secondly, ODOT and the City of Portland just got done with a planning effort including land use and transportation plans, and several years of negotiating. You can find out more detail if you'd like at the website below. We are proposing two lids (for a variety of reasons). One thing often overlooked as a benefit is lids offer great construction staging options.

http://www.portlandoregon.gov/bps/article/415777

Just thought I'd 1) brag (first time ODOT and City agreed) and 2) offer information if you'd like. SR 520 project in Seattle is also proposing many lids.

There are some nice watercolor drawings of freeway caps in the document. Watercolors can make any infrastructure look good though.