In the west of Germany, there is a string of major cities more or less in a line stretching from north to south. Almost 32 million people live in these cities or their metropolitan areas. I imagine it would be super useful for people living there to only have to pay a modest monthly fee for unlimited usage of all those public transport systems.

I live in the UK, and in London there is a unified public transport service. When I have to go on business trips to other UK cities, there are usually many different bus companies and sometimes if I buy a daily ticket for one bus provider then I can only take their buses. I would love a unified national ticket like this.