In my last post, I talked about the value of redundancy in transit networks. Connecting this back to our goals, I think this speaks more to the relative value of transit over cars. If you've got a robust transit network (thanks to commenter Most but not all on the last post for that term), you can compete with car networks that strand people if they lose access to their cars. If you have a sickly transit network, like the commuter rail lines that only run during rush hours, you'll lose people to cars whenever it's practical to drive.
One network in need of robustness is the Northeast Corridor train line from Washington, D.C. to Boston. If you want to go from Boston to Washington by train, you have to go through New Haven, New York, Newark, Philadelphia, Wilmington and Baltimore. As we saw with last year's Thames River bridge outage, there is a little bit of redundancy between New Haven and Boston provided by the "Inland Route" through Springfield, but even that is not electrified between Springfield and Framingham (I think), and is single-track for most of that stretch with heavy competition from freight.
I'm less familiar with the Delaware/Maryland area, although Wikipedia says there are three routes from Washington to Baltimore, all in good condition and currently used for passenger rail: the former Pennsylvania mainline currently used by the Northeast Corridor, the CSX Capitol subdivision used by MARC commuter trains, and the CSX Old Main and Metropolitan subdivisions, partly used by MARC. But if anyone has other ideas about pinch points there (and information about the electrification status of any of these lines), feel free to leave them in the comments.
Between Baltimore and New Haven there is simply no alternative to the mainline. Compare this to the Peter Pan buses, which routinely switch between Interstate 95/91 and Interstate 684/84 to get from New York to Hartford, depending on where the traffic flows better. This is not an argument for buses or cars, it's an argument against sickly, non-redundant rail infrastructure. There are tons of pinch points along the Corridor that would completely disable large sections of it. We've seen the Thames River, and I'll mention a few others and how we could get around them.
The first pinch point I want to mention is the Morrisville-Trenton Railroad Bridge over the Delaware River. However, there is a bridge just four miles upstream that is used for electrified SEPTA commuter rail from West Trenton to Philadelphia. The currently-unfunded project to reactivate passenger service from West Trenton to Newark would provide an alternative route for less than $200 million (plus electrification).
The next pinch points are the bridge over the Passaic River in Newark and the Portal Bridge over the Hackensack River in Secaucus. The century-old Portal Bridge is a known weakness and is due to be replaced in the next five years - but because it's so essential, the replacement project will be huge and complicated. There's also the Hell Gate Bridge over the East River.
But let's skip those for the moment and consider the weakest point in the whole corridor: the Hudson River crossing into Penn Station. Even if the ARC tunnel eventually connects to Penn Station (or even Grand Central), you've still got a huge amount of train traffic being routed through Midtown Manhattan. We could even consider the whole stretch from Newark to New Haven as a single, ninety-mile-long weak point. Currently, the nearest place where FRA-compliant trains cross the Hudson (other than the float bridge for freight trains) is Selkirk, NY, a little south of Albany. Passenger trains cross a few miles further up between Rensselaer and Albany.
As I've covered before, there are tentative plans to run commuter rail over the replacement for the Tappan Zee Bridge, but the focus is entirely myopically centered on "commuter rail" connecting the former Erie mainline at Suffern with the Hudson Line at Tarrytown. The (flawed) Tappan Zee process did consider running the line east to connect with the New Haven line in Port Chester, but rejected it because of low commuter ridership projections. The prospect of a more robust Northeast Corridor would bolster the argument for this new line.
I'll end it here for now. There's another idea I'll get to in a later post.