No further progress was made until 1930, when the BERy and BTD reached an agreement for a $350,000 station with four-car platforms. The cost reduction was achieved by having the platforms on the straight track west of Charles Street, rather than the curve to the east. Plans for the station were completed in July 1930. Bidding on the station opened in early July 1931, and a construction contract was awarded later that month. Charles Circle was completed in November 1931, by which time the steel structure of the station was in place in the center of the traffic circle. Charles station opened on February 27, 1932. The station was served by Bowdoin Square–Park Square and Charles station–Massachusetts station bus routes, though a Kendall Square–Bowdoin Square route was closed with the station's opening.