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.
Having wider tyres ~2"/50mm or so pretty much eliminates the risk (and gives a comfy ride). If you really like the speed of narrow tyres, it’s really quite safe with the right technique – crossing tracks at an angle to avoid mishaps (I find 30° is sufficient, 90° is never a problem), and when they’re slippery, treating them like ice. It becomes second nature soon enough.
I think there are some rubber/elasromer inserts which have been developed which also eliminate the groove – it presents a flat surface to bikes, yet squishes down for the tram wheel flange under the immense weight.
You’re looking at mountain bikes or the sturdier gravel bikes to fit 2" tyres. Your average commuter bike likely won’t have rhe clearance. And yes, even tiny 23mm road racer tyres can cross tramlines with the right technique, but the requirement of a proper technique is still a barrier to entry.
We’ve been calling for those rubber inserts, but so far to no avail.