Avenue around the east side of South Station, or headed west on Kneeland Street and south on Albany Street to one of the other Fort Point Channel crossings. The next change happened in the 1950s, when the Central Artery (now I-93) was built. From Broad and High Streets south to Dewey Square, Atlantic Avenue was made one-way northbound as a frontage road for the Artery, with southbound traffic using Purchase Street on the other side of the Artery. Atlantic Avenue was kept two-way south of Dewey Square, where through traffic used the Surface Artery. The Union Freight Railroad was abandoned in 1970, removing tracks from the center of Atlantic Avenue. Soon after, the road was realigned inland from Broad and High Streets most of the way to its north end, where it turned northeast and returned to its original alignment for the final block to Commercial Street, roughly along the old Mercantile and Richmond Streets. A short section of Old Atlantic Avenue exists in the original location between Milk and State Streets. When the Big Dig put the Artery underground in the late 1990s and early 2000s, the full section along the Artery, as well as the southern end, was converted to one-way northbound, with southbound traffic on the other side, known in sections as Surface Artery, Purchase Street and again Surface Artery. The new northbound tunnel was built under Atlantic Avenue south of Dewey Square. Only the part curving away from the Artery to end at Commercial Street remained two-way. South of Kneeland Street, a ramp from the northbound Artery and its frontage road joins the intersection of Kneeland Street and Atlantic Avenue. Railroads and other transportation By 1871, the Dorchester Avenue Railroad ran along Atlantic Avenue south of Broad Street (still called Broad Street at the time) as part of its route between downtown and Dorchester. However, 1872 and 1874 maps show these tracks removed in favor of tracks along Beach Street. An 1888 map appears to show tracks again, along the full length of Atlantic Avenue (ending at the Commercial Street merge), and an 1897 map shows tracks not only on all of Atlantic Avenue but also on Commercial Street towards North Station. In 1872, the Union Freight Railroad was built along Atlantic Avenue, connecting freight lines on both sides of downtown. It was removed in 1970. The 1899 extension of Atlantic Avenue also resulted in a