Not really on the street but the Subway Station by that name. It is where the F/G and the R cross. Currently to get to the F/G train one has to cross 4th Ave. if you are coming from Park Slope.
But look what I found behind a plywood panel.
The nice construction workers said is it only temporary because the other side is going to be overhauled. I don't think it will be so temporary. There is no reason not to leave it there after the other side reopens. Brooklynpix posted a nice photo of the construction under the El.
I a year or so this is going to be a much nicer and safer place. Check out this blog to see the present and future of the station.