I suppose that this will never ever work in Singapore, seeing how Singaporeans treat seats like they are the most important treasure in the universe, and how obnoxious, greedy, and selfish they are

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But I know that it works, at least in Japan. The Yamanote Ring line, a commuter rail line that operates like a subway looping through Tokyo, has trains with "cattle cars"; these have six doors per side (normal is four per side, like our MRT), and they run without seats during peak hours to pack in more people. I think it works most probably because Japanese people (again, at least, but I notice this in many other foreigners too) don't really care too much about seats - I still remember when I was on a route 54 bus once which was partially empty; there were these Japanese ladies who boarded the bus but didn't take the seats, but stood at the standing area (I was on a MB O405 bus) all the way from the Orchard area until somewhere near Liang Court.