the way to think of these is as instantly reconfigurable trains. in an ideal market, an enterprising entreprenuer would be able to install tracks on the most used routes and lower costs (and emissions). but we've long succumbed to corruption and financialization in markets (note that if risk is priced properly, capital wouldn't need to evaluate opportunities deeply, but would rather take every NPV-positive project available, in order of expected returns, in a large and diverse enough portfolio to mitigate systemic risk).