From Lombard-South station south to Snyder, the tunnel was constructed differently – only the eastern half of the line was built. The track currently used for southbound trains is actually the northbound express track. The extension in 1973 to Pattison Station (now called NRG Station) continued this arrangement. Space exists under the western half of Broad Street for the construction of the western half of the tunnel, which would include the remaining 2 tracks and additional island platforms for southbound local and express trains. The resulting infrastructure would match the configuration built in the northern half of the line.