[bdcravens]

Nation-based segmentation makes the most sense to me because as I understand it (coming from a US-centric perspective, so I may have misunderstandings) there may be additional friction (fees, regulations, etc) buying from another EU country as opposed to someone in the US buying a vehicle from a different state. In many cases, you don't even have to go to another state; dealerships regularly transfer inventory (with a shipping fee, but not anything at the government level)

[crote]

The entire point of the European Union is to eliminate all of that friction. Most of the rules and regulations have been pushed to the EU level, just like the USA pushed most of its rules and regulations to the federal level. A car only needs a single type approval granted by a single member state, and it can be sold across the entire EU.

There are of course still some tax differences and importing from another member state might be slightly trickier for a consumer than buying it from a dealership in their own country, but I don't see how that is any different from dealing with different kinds of sales tax in the various US states, or having to transfer your car title to another state.

The European single market operates as, well, a single market.

[rsynnott]

From the point of view of the manufacturers, the Single Market is, ah, a single market; they only have to get type approval once, and then they can sell anywhere. The only real complicating factor is Ireland and Malta, which drive on the left side of the road (and some niche cars will never be released there as a consequence; for instance Tesla stopped selling Model S/X in a left hand drive configuration a while back, though they now seem to have stopped selling both in Europe entirely, in any case).

Post-Brexit, the UK has its own type certification (and of course it also has the left hand drive problem), and, again, some niche car models may be available in the EU but not the UK. But in practice, for mainstream stuff, the manufacturers tend to treat it as just part of the European market.