Central Station and at North Station. Carrying a total of up to four tracks, the tunnels would have steep inclines. Trains entering or exiting the tunnels would climb or descend 3% grades, each nearly long. Because the tunnels would continue well south of downtown, three portals would accommodate separate connections to Back Bay Station to the west, the Old Colony Lines to the south, and the Fairmount Line running southwest. To the north, the tunnels would cross the Charles River about below its surface (bypassing an existing drawbridge), and connect via portals to the Fitchburg Line and the other northbound rail lines. The plan would require two or three new underground stations; stations are proposed roughly beneath the current North and South Stations, and possibly a new Central Station near Aquarium Station. Central Station would have an platform; North Station and South Station would have platforms. Pilings for a planned high-rise tower at South Station complicate a proposal to put the tunnels directly beneath the present South Station. Instead, the Dorchester Avenue Alignment proposal would move the tracks just east of South Station, and would build an underground facility about below the surface of the Fort Point Channel at the Summer Street crossing. Tracks at the underground South Station would have a 0.61% incline. The new Central Station would connect with the Blue Line at its Aquarium station via an underground concourse, as the Blue Line is the only rapid transit line in Boston that does not already connect with either North or South Station. The new station also would eliminate or reduce transfers to the rapid transit system for many commuter rail passengers with destinations in the central part of the business district. This would relieve transit congestion in the downtown core. Like Philadelphia's SEPTA system after the similar Center City Commuter Connection tunnel was built and connected two commuter rail systems, some of Boston's trains would be through-routed from one side of the system to the other. Many services would still terminate at North and South Stations, on existing tracks that do not lead into the tunnels. This could also allow trains to pass parked train cars. A 2003 DEIR/MIS assumes that about one-third of Amtrak trains to and from points south would be routed through the tunnel, stopping only at South Station, but with a new stop north of Boston at Anderson Regional Transportation Center in Woburn,