I dont know how are bus in your country but here they are really bigs and not rarely they drive 2/3 together what makes the traffic slowly and by read traffic light everything stops not only in the direction from the read traffic lights but in all directions because the bus blocks everything. If the all people in the bus drives a car the traffic would be more fluid.
I accept the bus makes less pollution but not better traffic.
When im a little late for work and i see a bus its done ..... at least 15m stoped in the trafic is guaranteed