I've known about this one for a few months, but it's just recently been completed, uncovered, and turned on.
The city of Alexandria got rid of an annoying stop sign on the Mt. Vernon Trail at the entrance to the Porto Vecchio Condominiums...a stop sign routinely ignored by cyclists and at an intersection that already had a traffic signal. What they did was replaced it with an "experimental" (per FHWA) bicycle traffic signal, the second one in the D.C. area (DDOT had "first honors", at 16th/U/New Hampshire NW in DC).
I noticed Monday that the Mt. Vernon Trail signal was finally uncovered and operating, so I went down and took a few photos. These and a few other photos are also in a Flickr set.
A southbound view of the new signal. Note that the "Bicycles Must Dismount" sign is still posted.
A closer view of the signal, looking northbound. Note the "Do Not Block Bike Path" sign for traffic coming out of the condos.
A close-up of the sign explaining how the signal works (in a nutshell, the same as a normal traffic signal).
And yes, just like a normal traffic signal, it turns red.
Of course, no bike ride would be complete without some idiot driver causing a blockage somewhere:
This was at Route 1 and Huntington Ave, where the vans were waiting in the left turn lane. The white work van in particular was pretty egregious.