"In Paris, I bought my Metro ticket and then used it in an
automated barrier to reach the platform. I noticed lowlife
furtively scanning the station and then vaulting the barriers, and
I saw armed police at the station to catch the thieves doing this
(they didn't catch any that I saw, and there were several of each
at each station).
"By contrast, the U-Bahn in Nürnberg has no barriers. I
bought my ticket, boarded the train without fuss, there was no risk
of being shot by a policeman targeting a barrier-vaulting cheat,
and the system was still clean, efficient and well-used..."