Considering that most of a city bus's use is at low speed, constantly braking and accelerating from stops, the hybrid should be a huge improvement environmental

Considering that most of a city bus's use is at low speed, constantly braking and accelerating from stops, the hybrid should be a huge improvement environmentally; it's the perfect use-case for a hybrid powertrain (where the ICE just runs at constant speed and charges the batteries, known as a serial hybrid vehicle).