Correction/clarification: the source referenced in the changeset comment is the MTA 2025–2029 Capital Plan, not a “2025 Capital Plan.” The Central Branch electrification project was included in the MTA 2020–2024 Capital Program but is not mentioned in the 2025–2029 plan; its status should therefore be understood as presumed deferred, not confirmed canceled.

I just want to first note with the voltage update for the New Haven Line—here and northward—that OSM's data consumers & renderers like ORM expect literal voltages (ex. 12500) rather than rounded classifications like 13000. Also, I find a contrast in specificity with the sources mentioned ("books" vs. the MNR G.O. in the changeset tags), and I'm not sure if I have the same access unless it's all on the Internet Archive or elsewhere.
Lastly: the overhead wires on the New Haven Line are tied into the Amtrak Hell Gate Line, which is tagged with voltage=12500. If there were a 500 V difference without a neutral section for separation, it would have, well... explosive results for any equipment trying to manage it.

I think you're right. My bad. I'll revert my edits accordingly.

I also didn't see that last comment while I was writing the one above. My bad.

Only 4 out of the 44 weekday trains on the branch (two round trips, or under 10%) are Midtown Direct runs to NYP. They exist, yes, but the other 40 run to Hoboken, and on weekends all service shrinks to an isolated shuttle terminating at Summit. Giving the track usage=main based on those peak trips doesn't reflect how the line actually functions.
Running longer trains exposes physical limits at the stations as well. Many platforms are only long enough for the 4-car Arrow III sets that comprise the vast majority of runs, meaning long peak trains forced onto short platforms inflate dwell times along the single-track corridor.

Lastly, the default OpenRailwayMap layer is explicitly titled "Infrastructure," distinguishing main lines (orange) from branch lines (yellow). Peak convenience trains routed onto the Morristown Line trunk at Summit don't make this a mainline west of Summit. NJ Transit itself publicly brands and timetables it as the Gladstone Branch.
The NYP runs are best captured in route=train relations as passenger services utilizing the branch infrastructure beneath them.

I appreciate the perspective, but I think we should ground this in established OSM railway tagging specs rather than passenger branding, as the wiki page for key:usage explicitly advises evaluating corridors individually by infrastructure rather than timetable titles:
"The distinction between main and branch line in general should be straightforward, but may be vague in certain circumstances... one should consider each case individually. Often, branch lines are described as such in the official name, however, sometimes rail is named 'XYZ Main Line' even though it is more appropriately tagged usage=branch."
Per the wiki:
usage=main is reserved for core trunk lines, primary corridors between major hubs, and routes carrying significant through-traffic.
Meanwhile, usage=branch is explicitly designated for secondary/feeder lines that diverge from a main line to connect outer communities or stub terminals, typically characterized by single track and passing loops.

West of Summit, the physical infrastructure matches usage=branch closely: it diverges from the Morristown Line (M&E) trunk, drops to a single-track roadbed with controlled passing sidings, and dead-ends at a modest stub yard in Gladstone that only has a few storage tracks alongside the single platform track for the station.

Visually on OpenRailwayMap's "Infrastructure" layer, giving Gladstone the same weight as the NEC, CSAO Lehigh Line, or the multi-track Morristown Line trunk flattens the regional hierarchy. Tagging the track west of Summit as usage=branch aligns directly with both the tracks and the OSM wiki criteria.

Thanks for adding that context with NJTRO’s documents! Given that I saw it on the 2015 Hoboken Division ETTs’ cover page, I’m going to add official_name=Gladstone Line and alt_name=Gladstone Line to reflect that, while keeping name=Gladstone Branch to reflect public-facing documents and schedules.
As for the usage tag, I’m keeping it as usage=branch to reflect the infrastructure hierarchy on OpenStreetMap and OpenRailwayMap. Even with such frequent service, the single-track layout and reliance on a handful of controlled sidings, plus the stub-ended terminus at Gladstone, all define it as a feeder branch off the multi-track M&E trunk rather than a network spine unto itself.