The WM established a connection with the Baltimore and Ohio Railroad (B&O) in 1892 with the opening of the Potomac Valley Rail Road (controlled by WM) between Williamsport and Big Pool, Maryland. This connection brought a major increase in through-freight traffic. Construction of an extension from Hagerstown to Cumberland began in 1903 and completed in 1906. This became the West Subdivision. To service the expanded system, the WM built a major shop complex at Hagerstown in 1909, with a roundhouse, machine shops and related facilities. Rail yards at Hagerstown were also expanded.