Hubway continues its expansion into Somerville this week as the bike sharing program installs stations in Davis, Porter, Powder House and Ball squares, according to Boston.com.

The Boston bike sharing program expanded into Somerville, Cambridge and Brookline in August, and the first four Somerville stations were in Union Square, City Hall, the intersection of Beacon and Washington streets and Conway Park.

The installation of subsequent stations—12 are planned for the city, in all—was delayed while Hubway waited for parts from the manufacturer.

After this week's installations Somerville will have eight operating Hubway stations, and according to Boston.com the locations of the final four stations haven't been determined yet.

The city previously pointed to Teele Square, Highland Avenue, Powderhouse Boulevard and eastern Davis Square as other likely locations.

Because Hubway is a network of stations that began in 2011 in Boston, it has to expand outward, with stations closer to the network's hub coming on line before stations that are further out.

Hubway shuts down during the winter, so there's not a lot of time left in the current bike sharing season.