OK. California owns 15 F59PHIs and 2 P32-8s. Amtrak owns 21 F59PHIs and 18 P32-8s.
Washington is replacing 8, Missouri is replacing 2, Illinois is replacing 4 on Lincoln Service, & Illinois is replacing 13 on other services, not counting the locomotives for expanded service; so that probably allows Amtrak to retire 27 locomotives.
California is buying 14 locomotives for Surfliner service and 6 for "unknown". If their priority is replacing Amtrak leased units, this should displace all remaining leased Amtrak-owned units -- and leave a bunch of additional locomotives, but not enough to replace their whole fleet. Expansion plans aren't going to require more than a couple of locomotives. Which California-owned locomotives is California going to retire? I'm guessing the P32-8s, but I've heard no word...
It's not a straight forward replace. All the Amtrak F59PHIs are used on the west coast. So the 15 Midwestern Chargers will be replacing P42s. Those P42s probably won't be retired but distributed elsewhere in the system.
While the B32s aren't that well loved for revenue runs, they are decently liked for yard service (which is what most are used for anyways) the P42s. Full-cowled/cabbed units are less useful for yard work (harder to reverse, harder to jump on/off, etc)
OK, I'm starting to figure this out. So with Cascades currently running 8 F59PHIs, California is running 13 F59PHIs owned by Amtrak, 15 F59PHIs owned by California, and 2 P32-8s owned by California. The other P32-8s, owned by Amtrak, are probably relegated to yard service or will be soon, and may be retired if there are enough P40s and P42s available for backup.
So California is buying 14 Chargers for the Surfliner; this replaces all 13 F59PHIs owned by Amtrak and adds 1. (For this calculation, it doesn't really matter whether the Amtrak-owned F59PHIs are running on the Surfliner or on the northern services, so I assumed for simiplicity that they were running on the Surfliner.) I'm not sure how many locos Surfliner uses as a whole, but 14 seems close to correct.
Meanwhile California is buying 6 Chargers for the northern services (Capitol Corridor & San Joaquin), which currently run various leased locomotives, 15 California-owned F59PHIs, and sometimes the P32-8s. I'm not sure how many California uses here, but it looks like 8 on the San Joaquins and 12 or so on the Capitol Corridor, maybe less, which adds up to about 20. So the 6 Chargers should replace P42s leased from Amtrak, because adding them to 15 California-owned F59PHIs gets you to 21. There don't really seem to be any for expansion.
So it looks like California will keep operating all or most of the California-owned F59PHIs on the northern services. Which means that Oakland will be stuck maintaining F59PHIs for California after Amtrak has stopped using them. Curious.
It's not clear to me what happens to the California owned P32-8s, but it seems like they probably won't be used in regular revenue service. Relegated to yard service? Does California really have a use for them? While running HEP they have relatively poor power and California wouldn't want to use them on the Surfliner. Apparently they're sometimes used on the Capitol Corridor, but that doesn't seem very desirable either.
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Anyway, if we assume that Amtrak has no further interest in its displaced F59PHIs (apart from possibly leasing them to states), and that the P32-8s are already not used in routine revenue service any more, this also allows us to figure out how many P42s are "freed up" to provide spares and relief for the trains which will continue to run P42s. The answer is 2 from Missouri, 4 from Lincoln Service, 13 from other Illinois, and 5 or 6 from northern California service. So about 25. This should help with the ability to keep the P42 fleet running reliably... for a few more years.