I know that this topic has been brought up on Archinect before, but since I can't find the thread, I'll contribute:

May I present: Burnside skatepark

http://www.skateoregon.com/Burnside/Burnside.html

Sorry, it's a bridge, but I thought you might still be interested.

this shi* ain't cool. it keeps lots of drunks occupied enough while driving to dent local cars. it's also one of the top spots for suicide in seattle, with people landing on the adobe parking lot...
unfortunately, AWB along w/ city of seattle want to keep people from jumping. the only logical thing to due is actually prevent people from walking across the bridge, but instead, they're going to put some ugly contraption below to catch those that wish to end their life. probably the only time i've been a total 180 from AWB.

lots of inhabited areas under elevated highways, railways, or bridges in paris or tokyo that i have seen. one of my fav places is area around nihonbashi...very cool looking, though imhabited by river rather than people...still, go round the road a bit and there are shops under most of the elevated bits around tokyo station. try googely.

Milwaukee has been working to build things under 794 between downtown and the Third Ward. A market and a nature center so far.

there's a night rendering of a japanese project in which little round dwellings are suspended from the highway - somewhere in the image gallery. haven't been able to find it this morning here in the office, but i have it saved at home.

In Buenos Aires there are tons of basketball, tenis, soccer courts under overpasses...quite ingenious.

a lot of fires seem to happen under them...and fires are not cool

fire is actually really cool.

NL Architects' additional program under the A8 viaduct. Too lazy to post an image: [ulr=http://www.nlarchitects.nl/]NL[/url]

murals of local heroes
Echo Park
Under the 101


Katherine Spitz & Associates
Santa Monica
Under the 10


George Hargreaves with Julian Lang, 2001
San Jose
Under the 280 and 87

channel street skatepark in san pedro (LA)

i have always liked this number from Odile Decq + Benoit Cornette,
motorway control center offices.

blowjobs???

also FDR skatepark in philly under 95

Saturday Market in Portland, OR

and I believe it's called Washington Jefferson Park in Eugene, OR

mdler, no, but thank you for asking. Have a Happy Valentines, anyway!

What's wrong with leaving them as shelters for the homeless or hideaways for drug deals?

I agree aquapura - sometimes for the chronicly homless the overpass is the only shelter they can find. In Chicago theyve fenced them all in - it really weird, I thought it was kind of cool there were little cities under the Kenedy xpwy. Not any more. When I was kid we played under the 290 viaduct throwing bottles of gas at freight trains. Maybe thats partly why they fence them in now. I dont know.