It was the first transfer station on the system to receive the "Under" postfix, rather than a separate name from the existing station. This represented a change in naming policy, and the first step towards easing wayfinding difficulties in the complex system. North Station West (opened later in 1912), South Station Under (1916) and Scollay Under (1916) would later use this naming scheme. Construction of the Dorchester Tunnel begun on May 3, 1912; this extension opened to Washington on April 4, 1915, and in three more segments to South Station Under in 1916, Broadway in 1917, and Andrew in 1918.