>>941084>implying individual countries are not able of making an agreement about border controls on their own^this.
There's a bus line that crosses between Windsor, ON and Detroit, MI that's been running for years and if this can be tolerated by the border obsessed Americans then I don't think there's going to be a problem even on the off chance the Schengen zone ceases to be.
Hell, there were also a bunch of international tram lines in the US right up to the 1970s.
>pic related 