Can you try to mention your sources explicitly? I mistakenly reverted a similar changeset recently because it gave the impression of being based on out-of-date imagery and nothing else; I put it back to an alignment that looked consistent with the most recent Maxar Premium imagery, but was based upon a misreading of that imagery (as I've since discovered in-person).

I've had another look at the both the plans and the current state of the road, and it looks like I was probably misreading the aerial imagery. Greyseal18 has put this back roughly how you put it here; apologies for my mistaken reversion. However, it still isn't clear to me how you knew the correct alignment - could you try to be more explicit about sources in the future to avoid unnecessary reversion?

Those roads look like trunk links to me - there is no way of driving along them without either coming from or going to the trunk road, and no property accesses or anything like that. Technically I think a cyclist could use those links, but since a parallel cycle route exists I don't think that should prevent it being marked as trunk_link.
I also think that the section of Leaf Lane north of Black Prince Avenue is mismapped - Mapbox and Esri World imagery both seem to show the central white line continuing round from Black Prince Avenue, implying that Leaf Lane is two-way for the stretch adjacent to numbers 87 and 89. Beyond that point I think it becomes a trunk_link too.

On what basis did you make this change? The changeset comment says that you used Bing imagery, but this provides no evidence for this alignment. More recent imagery is available from Maxar, and this was mentioned when I originally corrected the alignment of the road in changeset/71993430. I've reverted this changeset, since it contradicts the evidence in the Maxar Premium imagery, and the changeset comments suggest no firmer basis for making this change than "having the carriageways adjacent on the map looks neater".

The combination of this change and the previous change has created a new way that replaces the original way for the start of the history - this effectively hides most of the history of that way. In future, when merging ways, try to keep the one with the most informative history - especially if the other one was one you just created.
Also, I have no idea why you set part of the A1307 slip road as 'trunk' instead of 'trunk_link' - it seems obviously wrong to me.

You've made a few mistakes. You've left the old J31 slip road marked as open, and you've broken all the Citi 5 bus relations. Admittedly, I'm not 100% sure what the new outbound routing will be, but I could at least make a reasonable guess and check tomorrow. (For the eastbound changes, I had intended to just revert my previous edit to save the hassle of reediting the inbound bus routes.)
Also, I don't think I agree with editing the map 48 hours before reality (or more if plans change).

The opening of the new slip road was announced in https://www.facebook.com/A14C2H/photos/a.238494069903679/693911841028564/. Based on comments and an educated guess, I would expect the temporary slip road to use a bit of the new main carriageway as well, but since I don't yet know how much, I just drew it as leaving the existing carriageway at the latest possible moment to meet the eventual permanent slip road.

This was drawn mostly from what I saw when I visited the sight previously, along with some educated guesses, so anything derived from ariel imagery will be much better. However, with both the new WB carriageway and the first of the two exit slip roads both being constructed to the south of the original A14 route here, I don't think it is possible to deduce the alignment from the Maxar imagery, which is still relatively old at this point. I intend to revisit this area during the next week to get a better look (although I am limited in what I can safely access without a motor vehicle) - I expect combining a site visit with the Maxar imagery will give better results that using either one alone.

Are you sure? I can't find anything on Twitter to suggest it will be single carriageway, but I do find this tweet from just before your changeset which has a diagram showing a dual carriageway here.
https://twitter.com/A14C2H/status/1092403677166477312

I don't understand this edit. You claim to be using Bing as a source to improve the mapping of an underground railway - I can see how this could work for the cuttings (although you should be careful to avoid introducing paralax errors), but parts of your edits involve tunnels that wouldn't be visible in satellite imagery. Can you explain how you made these edits?
You have also made a couple of clear mistakes in this. Firstly you've added ways 654075521-654075533, which I presume you added temporarily to preserve track spacing - these should be deleted. You've also distorted some buildings by moving nodes that form part of their boundaries - you needed to split these nodes into separate nodes for the building and railway, and restore the building node to the correct location. (These nodes shouldn't have been shared by the railway and building in the first place, but you should watch out for mistakes like that when making updates.)

I've now read more of the Highways England Strategic Road Network Initial Report, and it seems that I was previously misinterpreting it. According to the report (P58-59), the highest classifications of roads will be "Smart Motorway", "Motorway", "Expressway" and "All Purpose Trunk Road", with expressways differing from smart motorways only in the typical number of lanes (2 instead of 4) and the typical designation (A*(M) instead of M*). I had previously read only P78, from which I incorrectly inferred that 'expressway' referred to only phases 1-3 in that description, whereas I now believe those are pre-expressway.
(Since I presume you've already read that document, I write this more for the benefit of anyone else reading this.)

Can you provide some evidence of this? The only documents I can find online relating to this suggest that it might become an 'expressway', which is not (initially, at least) the same thing.