In 1941, the Boston Elevated Railway bought the BRB&L right of way from Day Square to Revere Beach for use as a high-speed trolley line similar to the Ashmont-Mattapan High Speed Line; these plans were delayed by the onset of World War II.
However, the 1926 Report on Improved Transportation Facilities and 1945–47 Coolidge Commission Report recommended that the East Boston Tunnel line, which had been converted to rapid transit from streetcars in 1924, be extended to Lynn via the BBRB&L route rather than using it for a trolley line.

In 1947, the newly formed Metropolitan Transit Authority (M.T.A.) decided to build to Lynn as a rapid transit line, and construction began in October 1948.
The first part of the Revere Extension opened to Orient Heights on January 5, 1952.
A one-stop extension to Suffolk Downs opened on April 21, 1952 - the first day of the racing season.
The station had only one track and one platform until the second phase (cut short due to limited funds) opened to Wonderland on January 19, 1954.
In 1941, the Boston Elevated Railway bought the BRB&L right of way from Day Square to Revere Beach for use as a high-speed trolley line similar to the Ashmont-Mattapan High Speed Line; these plans were delayed by the onset of World War II. However, the 1926 Report on Improved Transportation Facilities and 1945–47 Coolidge Commission Report recommended that the East Boston Tunnel line, which had been converted to rapid transit from streetcars in 1924, be extended to Lynn via the BBRB&L route rather than using it for a trolley line.
In 1947, the newly formed Metropolitan Transit Authority (M.T.A.) decided to build to Lynn as a rapid transit line, and construction began in October 1948. The first part of the Revere Extension opened to Orient Heights on January 5, 1952. A one-stop extension to Suffolk Downs opened on April 21, 1952 - the first day of the racing season. The station had only one track and one platform until the second phase (cut short due to limited funds) opened to Wonderland on January 19, 1954.
Suffolk Downs station