One advantage of LRT is flexibility. It can go to downtowns, even historical areas where an elevated structure may be undesirable. Signal pre-emption can increase average speed. Without a doubt, the bus is the loser. Buses are also more expensive to operate.
Buses are slower than automobiles since they are stuck in traffic.
For these reasons, General Motors acquired transit and electric train companies and substituted buses for both streetcars and trains. Transit patronage dropped drastically after the destruction of guideway transit. Each guideway transit modes has certain advantages, and we need them all in the niches they perform best. When transit advocates attack one mode over the other, the winners can end up being the highway lobby. While commuter rail and PRT advocates both attacked BART recently, they stayed mum on the highway projects.