Even if you think what you would say is obvious, please add. This is genuinely something I think makes sense regarding local bus routes given the longevity of light rail and how infrequently routes change, but I also suffer from confirmation bias, so I’m hoping for reasons this would be a terrible idea but obviously would prefer reasons it would be an even more amazing idea than I thought.
Rail has some advantages. Efficiency, Tyre dust. Long term cost. It’s a bit harder for the next government to dismantle it. Higher capacity, more predictable path/easier to give intersection priority. Much much easier to automate if given dedicated right of way. Better accessibility.
Rubber wheels have advantages too. Quieter, more flexible (especially with a buffer battery), lower per-vehicle cost can increase the number of services.
I think the first goal should be getting any service that doesn’t get stuck in traffic. Then grade separation and consider the tradeoffs for rail.