I can't find a cite, but I read an article somewhere that some transit fare systems work like that. Each node tracks every customer's balance and broadcasts tr

I can't find a cite, but I read an article somewhere that some transit fare systems work like that. Each node tracks every customer's balance and broadcasts transactions. That's how the turnstile is always able to respond instantly, because the validation is local. It's possible to duplicate a card and swipe it simultaneously at different stations to double-spend. It's considered an acceptable leak in the system given the high effort, infungibility of the good, and near-zero actual cost of a free-rider. Where subways diverge from Bitcoin is that sold goods can represent a real loss, can be resold thus creating the incentive to scam, and that Bitcoin is anonymous where subway cards aren't (security cameras) so repeated instances of this crime can be caught. So the consequences of double-spending with Bitcoin are vastly higher and the network can't just choose to live with it.