FASTRACK work is affecting the No. 4, 5 and 6 trains operating in Midtown to Downtown Brooklyn during the overnight hours.

According to the MTA, the FASTRACK program involves devoting four straight weeknights to perform maintenance work in tunnels, stations and on tracks, completely suspending service within a given line segment for a seven-hour period between 10 p.m. and 5 a.m.

During that time, there will be no service on the No. 4, 5 and 6 trains from Grand Central 42nd Street to Atlantic Avenue/Barclays Center. No. 3 train service will be extended to New Lots Avenue, and six trains will operate between Pelham Bay Park and Grand Central 42nd Street.

Some travel alternatives include the No. 2, N or R trains.

The changes will be in effect until Friday, Feb. 26.