I wondered the same thing. There's cities changing R1 to R3 or R4, and the infrastructure wasn't stopping them. On the other hand it might necessitate upgrades

I wondered the same thing. There's cities changing R1 to R3 or R4, and the infrastructure wasn't stopping them. On the other hand it might necessitate upgrades if all R1 units are converted to R3, but then you have three times more taxpayers per mile to pay for that infrastructure.