SEPTA was easy! The same agency was running trains on both sides of the tunnel with equipment that was compatable with each side. Here you have three different agencies, plus Amtrak in the middle, all running equipment that by and large is incompatible. You are also involving three different states that each have their own priorities.
The expense is huge and they will never reach a deal on who gets to throw away their equipment and buy new equipment that is compatible all around. Heck, even now we can't share equipment between the LIRR and MNRR, and they have the same parent. The costs of throwing away all the new equipment, as well as the old, is simply too great.
But SEPTA's system was originally one railroad on each side.
Are there any dimensional problems with running NJT equipment on MN's ROW or vice versa? (Let me guess, MN ordered equipment that won't fit through the old PRR tunnels?)
If you start with connecting two tracks from the old NYP to the lower level of the old GCT, and it takes ten years to build it from when it's planned, there's a decent chance that some of the equipment (which probably has a 30 year lifespan) was going to be replaced while the tunnel was being constructed anyway. And the older equipment could be used for the stub end routes that don't go all the way across Manhattan until it wears out.
Metro North probably would not have any problems with the equipment fitting through Penn and the old North River tunnels. However I'm not so sure that any of NJT's equipment would fit into the Park Avenue tunnels, certainly the brand new still being delievered multi-levels won't fit.
However the bigger problem is that the propulsion technologies are different for each RR. Of the Metro North equipment, the only cars currently capable of operating into NYP are the ones that run on the New Haven line. And at most, that represents 1/3 of MN's entire fleet. All the cars on the Harlem and Hudson lines at present cannot operate into NYP, much less into New Jersey. Only the New Haven cars can pull power from an overhead catenary.
And while there is third rail in all of NYP, it ends shortly before the North River tunnels pop up in New Jersey. Additionally, MN's third rail is incompatible with the LIRR's third rail, which is what exists in NYP and the North River tunnels. MN uses an under-running shoe to pull the power off the rail, whereas the LIRR uses an over-running shoe to pull power off the third rail. And no technology exists to install reversible on the fly shoes and I rather doubt that it can be invented without huge expense, if even then.
Turning back to NJT, they die as soon as they reach GCT, since there is no catenary in the Park Avenue tunnels and no room to install catenary in those tunnels. Similarly the LIRR can't operate into the existing GCT because of the shoe issue, and they can't operate into NJ because the third rail ends just as they exit the tunnels.
So it's not just a matter of attrition on equipment, attrition that won't help all that much anyhow at least with a 10 year window, since all three agencies have probably replaced at least 50% of their fleet within the last 5 to 8 years. It's a matter of someone biting the bullet to install the other's technology and then finding dual use cars to use, at least until everyone is on the same technology.
Throw Amtrak into the mix, who isn't going to want to replace the catenary with something else, and that pretty much means that NJT would have to install third rail throughout their entire system so that MN and LIRR can operate into NJ, and then either the LIRR or MN has to replace their third rail system with the other's third rail system.
We're talking Billions of dollars, if not a Trillion or more, for little benefit IMHO. Having a cross town connector would be something that I would support and could see both happening and being very useful. Trying to integrate all three systems so that 80% of all the trains run can operate from one state to the next simply isn't worth the effort and the money for the small amount of people that would actually use it. Are there people who could take advantage of an NJT train that ran to say White Plains or Babylon? Most likely, yes. But there aren't enough of them to warrant the expense. Better to simply have them make a transfer at either Penn or GCT to accomplish that, than to spend Billions. The benefits don't outweigh the costs.
Or some of the 20 year old equipment could be sold off to some other city that's starting up commuter service. Connecticut may be extending the commuter runs past New Haven towards Hartford, which might help to create demand for some of that older equipment, too.
Most of the current MN equipment that would become available is incompatible with the diesel hauled trains being considered for New Haven to Hartford and beyond. One can’t haul MU trains with a diesel engine in revenue service.
There is also some evidence that MN can cooperate with NJT in that there are some lines that are technically MN lines operated by NJT into Hoboken. Is the MN equipment used for that the same as the Hudson Line / Harlem Line equipment?
No, the MN equipment used for the joint service basically matches NJT’s diesel hauled operations elsewhere in NJ. It is not the same, nor is it compatible with the MU’s used on the Hudson & Harlem lines, or even the MU’s on the New Haven line. Once a track connection is built, assuming that ARC is built and NJT obtains the dual mode locomotives that I believe are now on order (it might still be at the RFP phase), those trains will be able to operate into Penn. But they won’t be able to operate into GCT because of the third rail issues.
One final thought on SEPTA, when they built their run through it was rather easy by comparison. You’re talking about knocking out four holes in a station wall, with no tracks in the way. Then building a half mile tunnel or so, that basically runs straight for most of it’s distance and didn’t have multiple subways, an underground auto tunnel, and a water tunnel in their way. With NYP-GCT you’re talking about a mile and a quarter run, with a big turn and all of the aforementioned issues of subways and tunnels.