From Dave Brigham:
I've ridden under this rusty old bridge countless times over the last several years. Located in Brookline, Mass., along the D branch of the Green Line trolley service, the Carlton Street Footbridge has been closed for more than 40 years. Talk of restoring and reopening the span has gone on for about half that time.
Built in 1894, the steel "pony truss" bridge is about 75 feet long, with staircases at either end bringing the length to 110 feet, according to this article in the Brookline Beacon (read the whole article for complete background and old photos).
The above cited article, written last November, states that the renovation project is under way, with a design completed that calls for access ramps at either end and new decking. The article indicates that working specifications and bid advertisements were next in the process; I'm unsure whether those have taken place. There are, of course, those opposed to this project.
Once begun, the project is slated to take approximately two years; the trolley service would be suspended for two weekends at some point, to allow for the span to be lifted out, and then put back in place.