Citi Bike will add 1,250 bicycles and 2,500 docking points to the busiest parts of its existing service area starting next spring, the de Blasio administration announced today. The extra capacity will help absorb a surge in demand when the western portion of the L train goes down for repairs.

The expansion will also include Citi Bike’s first electric-assist bicycles, 1,000 of which will be available exclusively at four stations — two in Williamsburg and two in Lower Manhattan. The e-bikes are specifically intended to help people handle the incline on the Williamsburg Bridge (Citi Bike operator Motivate calls it “Shuttle Service”). City Hall says these e-bikes are a temporary addition to the fleet available only for the duration of the L train rehab, which is expected to last 15 months.

The extra docking capacity will be concentrated in northern Brooklyn and Manhattan between Canal Street and 59th Street, the area most heavily affected by the loss of the L train west of Bedford Avenue. In addition, Citi Bike will send out several more valet crews to receive bikes from people at the end of their trips, adding capacity beyond the limits of docking stations at busy rush hour locations.

Before the new stations arrive, DOT will conduct a round of outreach with local community boards in the affected areas. Needless to say, these are all neighborhoods where sidewalk space is at a premium and bike-share stations in the curb lane make the most sense.

With each Citi Bike averaging about six trips per day during warmer months, the addition of more than 2,000 bikes for the L train shutdown could handle 10,000 or more daily trips (the limited e-bike origins and destinations may dampen trips-per-bike). Bus service will carry the lion’s share of the 80,000 or so L train riders expected to divert to surface travel instead of other subways, but Citi Bike will be a significant part of the mix, relieving pressure on the shuttle buses operating between Williamsburg and Manhattan.

City Hall’s announcement mentions no public subsidy for this bike-share expansion, and Streetsblog has a request in to confirm that Motivate is shouldering the costs.

As encouraging as it is to see the de Blasio administration and Motivate reach a deal on infill expansion for bike-share, it also raises the question: Why won’t the mayor push for a Citi Bike expansion beyond the borders of the current service zone?