I wouldn't necessarily say the utility is diminished — it's more like a tradeoff. If you want to repeatedly transport people in bulk, you need to follow a prede

I wouldn't necessarily say the utility is diminished — it's more like a tradeoff. If you want to repeatedly transport people in bulk, you need to follow a predetermined path. Even buses tend to follow fixed routes, despite not operating on rails. Commuters would be disoriented if the E train in NYC took a different path each day for example. So if you're following the same path every day, you probably don't need a complicated steering system, rubber tires that constantly wear out, and a large expensive battery. It's simpler to just have the vehicle operate on rails, and supply power through the third rail. Otherwise you end up with a bizarre situation like the "Vegas Loop", where you have cars driving back and forth along a predetermined path, lugging heavy batteries around with them.