The project began Monday night into Tuesday, meaning Manhattan-bound lanes of the bridge will be closed during overnight hours.
On weekdays, the lanes will be shut down from 11 p.m. until 6 a.m. On Saturday, they will be closed from midnight to 7 a.m. and on Sunday from midnight to 9 a.m.
The Brooklyn-bound lanes will remain open.
Construction crews will begin replacing rotting pavement. They will also repaint the steel to help prevent corrosion.
When the project is finished in 2014, the ramps to the bridge will safely handle twice as much traffic.
All Manhattan-bound traffic will be detoured to the Manhattan Bridge or other crossings. There will be no closure of the pedestrian/cycling promenade.
The bridge will be reopened for traffic in both directions each morning.
A downloadable brochure showing detour routes and closure dates and times is available at: http://nyc.gov/html/dot/downloads/pdf/brooklyn_bridge_brochure.pdf