The Gowanus Expressway, especially the section that is above the Gowanus Canal, has been under construction for the last 20 years. While they have expanded and rebuilt sections of the expressway, the road surface is in HORRIBLE condition. Will this ever be paved? Hey Bloomberg, how about fixing this!
The attached photo is the reason why you always see construction on the Gowanus Expressway. Its old, and its a very big structure to maintain. It is under constant repair via contracts awarded by the NYS DOT which owns I-278. These contracts are also partially funded by the federal DOT since it is an interstate highway. So, not to defend Bloomberg, but this isn't his problem.
The work is performed in stages to minimize the effect on live traffic. Rest assured, they do pour a new concrete road surface at the completion of each stage.