The Seattle Bus Tunnel carries both rail and buses, which is a bit of an operational problem. You are already aware that the Seattle experience is that it takes almost 6 times longer to remove a disabled LRT vehicle. Obviously another LRT vehicle was unabled to removed the disabled vehicle as you suggest. Removing a bus is very easy and as Seattle has indicated they now have a system that removes the disabled bus in less than 10 minutes. No need for sidings!
Bus breakdowns are a function of maintenance of the Seattle Transit Authority. Poor maintenance may be the reason for the breakdowns and that is why maintenance is so important.
In any case, all the future transit technology improvements are in batteries. Already there is a new bus being produced in Colorado that is totally operated on batteries and can go 50 kilometers on a single charge which is recharged in 5 to 10 minutes.
In any case rapid transit buses will ultimately be all battery driven and will command a maintenance priority. I am infomed that they are prototyping a lithium battery that will give over 80 kilometers on a single charge.
Rail technology belongs to a former era.
As the most repsected mass transit expert in North America, Randall O'Toole says: "LRT is a giant hoax that makes contractors rich and taxpayers poor"