The mayor announced last week that construction on a new protected bike lane for the Brooklyn Bridge — one that will take up a west-bound lane on the current roadway — will start this week. So far it seems quiet over there, but the work is scheduled to be completed by early fall by the city Department of Transportation.

The innermost Manhattan-bound vehicular lane will be transformed into a two-way protected bike lane with a concrete barrier between the bike and car lanes. Pedestrians will get the entire elevated walkway to themselves. The mayor said that this is the first major reconfiguration of the bridge since 1950, when trolley tracks were permanently removed.

However there’s a catch: the bike lane is only 8 feet wide total, or 4 feet in each direction — on the narrow side; the typical bike lanes on city streets are 5 feet wide.

So NB if you are driving home: Starting this past Monday, the right turn from westbound Tillary Street onto the Brooklyn Bridge will no longer be permitted — and I think this may be a permanent change. The city is also rehabbing the triple-cantilever section of the BQE, which will add to the delays.

During construction, cars can access the bridge from downtown Brooklyn via Adams Street and Sands Street, and the promenade will remain open to pedestrians and cyclists. Diversions are expected to move traffic in Downtown Brooklyn to both bridges along Gold Street, Nassau Street and the Flatbush Avenue Extension.

An interesting factoid from the mayor: when the bridge had trolleys, it carried 400,000 people every day. Now that it is strictly cars, there are more than half as many daily bridge users. The city predicts that the bike lane will increase the capacity of the bridge. (Hmm…light rail anyone?)

The bridge is 138 years old as of this year.