My guess is that busses don't use sensors in the lane but rather a radio signal. Which makes sense because it's flexible with regards to speed and which direction the bus needs to go. And not all intersections have dedicated bus lanes.

🚨 are useful, but red lights add a lot of safety. 

 Not if their hacked. Expected safety can be more dangerous than no safeguards, because people pay more attention 

 Offline but reachable by short range radio seems like a fine compromise to me. It requires physical proximity to mess with, which doesn't scale and is relatively easy for police to investigate. Just modernize the encryption. 

 Yes, that sounds acceptable  

 But that thought idd crossed my mind too. I just wonder why innovation often leads to more complexity 🤣