If you are living in the US you would be falling from your chair by now or just think that this is a joke. No, this is EID land Belgium and they didn't learn anything from what has happened to the social security number in the US and all the problems that arise from that universal use as an Unique Identifier.
So on the site of our national railwaycompany they are so proud to have found the egg of columbus. They have in fact to find a way to link your electronic ticket to your Identity and have some real proof that you are the same person sitting before the controller.
They have decided to use the National Register Number (which is the same). How the privacycommission could agree to something like that is a big question because normally the privacycommission is very reluctant about the use of that number - just because it is an unique identifier. But as the privacycommission is an institution without enough money, resources and political cloud and in which you can find as advisers the same people that have to decide about their own projects (ehealth for example) you shouldn't be surprised that you can do whatever you want with our national register number. source
And so your national ID unique identifier is becoming without any legal basis or protection or overview an Unique Identifier for a lot of things and applications. This way Identitytheft is becoming nearer at an increasing speed.
For privacyadvocates it is also worrying that electronic traintickets can be identified and linked to a person. If you have problems with that, don't use electronic tickets. Less electronic is better privacy.