I know we in Boston tend to look askance at ideas from elsewhere, but why is all the electrification around catenary? Metro North seems to have done decently well with third rail. Couldn’t the T crib from them, up to and including grabbing EMUs off the shelf from Kawasaki?
1) We already have 25 kV AC overhead on the Providence Line, the most common mainline rail electrification voltage in the world with standard parts available both lineside and vehicle-side. Why would we ever want to make things
harder on ourselves by adopting something incompatible with that for the buildout?
2) Third rail is significantly more expensive to build out at long distances. The DC voltage is much lower because of proximity to the ground, topping out around 750 volts vs. the 25,000 volts you've got on the NEC overhead. Lower voltage means you have to build
many more substations, about one every 5-6 miles vs. one every 30 miles. Substations are the most expensive by far part of an electrification scheme.
3) Third rail does not allow for very high speeds. 80 MPH average, 90 MPH max before you're simply grinding the third rail shoes to dust. Pantographs can do 200 MPH with no issues whatsoever. While I'm no fan of TransitMatters' 100 MPH systemwide proof-of-concept for lots of technical and hidden-cost reasons, you absolutely can't aspire to something like that (or even take advantage of using existing Providence Line track classes) at all with third rail.
4) It goes without saying that third rail is very dangerous around grade crossings. Dangerous for cars and pederstrians, and dangerous for trains. Metro-North had a nasty fatal accident on the Harlem Line in 2015 where a train derailed while striking an SUV at a crossing and several passengers on the train died when a segment of live third rail punctured the floor of the train.
5) Metro-North's EMU's are not "off-shelf". They and their LIRR sisters are some of the most overcustomized in the world for LIRR's uniquely small loading gauge and the tri-voltage complexities of the New Haven Line stock. They're overweight, overly pricey, incompatible with curved full-high platforms (which we have) because of the quarter-point doors, and incompatible with low or mini-high platforms because they lack door traps. We would never be looking at M8 or M9 clones as a starting point for our own EMU's.
6) Metro-North third rail is a
constriction for system expansion. To wire up to Albany for NYHSR you'd have to rip out all the third rail on the Hudson Line from Spuyten Duyvil Jct. to Croton-Harmon, replace it with 25 kV overhead, and order New Haven Line M8 clones...leaving only the city itself (necessary, because Park Ave. Tunnel + Grand Central Terminal clearances don't allow for any overhead of any voltage) as third rail. You wouldn't be able to extend third rail to Poughkeepsie for regular service because it'd be too many more substations for the cost vs. the 25 kV option, and to wire up diesel territory on the Harlem Line you'd probably need to do the same because the number of substations required to run an electric schedule to Wassaic (the 1984 North White Plains-Southeast electrification extension section is already notoriously underpowered for its loading, restricting schedules). LIRR can expand out OK because they're a geographically isolated system with only 1 connection (Penn Station) to the outside world and Long Island is already blanketed with a thick-enough net of traction power line interconnects meaning their substation builds are about as cost-controlled as they're ever going to get. But Metro-North literally
can't electrify any further within an acceptable cost if they stick with 750V DC third rail.