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.
Street level is not the same thing as “among car traffic”. For instance, there’s a stretch of the N-Judah in SF between Embarcadero and 4th & King which is on street level, but in fact it is in an entirely separate right of way, where it is illegal for cars to drive. And unlike other places in SF where it’s illegal for cars to be (like bike lanes, bus lanes, Market st), people actually respect that. So it’s entirely possible to avoid the private car right of way. If you can avoid intermingling with cars, and you get signal priority, then you’ll go faster than cars, because you’re not stuck in traffic and you don’t need to wait for the lights.
The issue is that in this segment, I haven’t noticed much in the way of signal priority. The N, which is far more important than any private car on those intersections, has to wait when it really should just sail through intersections, because the signals knew the N was coming and changed ahead of time.
I know that this can be achieved more or less with BRT, but it seems absolutely silly to put in the rails without having a dedicated right of way, and yet that’s what the majority of SF’s above-ground light rail is. IMO, if there’s light rail on the street, either it should be car free, or the railway should have curbs surrounding it to prevent intrusion from cars. Full stop.