The Arborway begins at a large rotary that connects it with the Jamaicaway, and curves past the main entrance of Arnold Arboretum (125 Arborway), where on-street parking is allowed. The roadway once continued through Forest Hills to the edge of Franklin Park, but now ends at the South Street border of the Arboretum. From there, traffic may either exit into Forest Hills next to Forest Hills Station or may continue onto the overpass towards Roxbury and Mattapan, Massachusetts.
Named Monsignor William J. Casey Overpass in honor of a Depression-era priest of St. Thomas Aquinas Church in Jamaica Plain, the Overpass was constructed in the mid-1950s to allow the increasing automobile traffic of the day to bypass the north-south traffic on Washington Street, South Street, and Hyde Park Avenue. In recent years, community groups have been investigating the possibility of fixing this "missing link" in the Emerald Necklace.