>passport checks ... between other EU countries The passport checks have nothing to do with the EU, it's the Schengen treaty[0] that allows omitting that part.

>passport checks ... between other EU countries The passport checks have nothing to do with the EU, it's the Schengen treaty[0] that allows omitting that part. Norway is a part of the treaty, so is Iceland for example. Some EU countries still don't meet the criteria to join, e.g. Romania, Bulgaria. Ireland and the UK are/were outside (voluntarily) of the treaty as well - which is one of the weirdest parts of the Brexit with the UK actually checking its own borders more than most of the rest of the EU. For example traveling from Poland to Norway by car (and ferry Tallinn - Helsinki) requires zero passport/id card checks. (id cards are a valid traveling document within the EU and Schengen) [0]: https://en.wikipedia.org/wiki/Schengen_Area https://en.wikipedia.org/wiki/Schengen_Area