The most significant emissions reduction will not come from the vehicles; it will come from people leaving their cars at home.
Let’s take the example of a Mexican commuter who chooses whether to ride a bus or drive to work each morning. If she drives, her commute will generate 8kg of CO2, vs. only 1.5kg when riding a diesel bus. By making the greener choice, she is saving up to 6.5kg of CO2. With a hybrid bus, that same ride would emit 1kg of CO2, and zero emission with an electric (assuming zero-emission grid)—translating into additional savings of 0.5kg and 1.5kg over a diesel bus, respectively. The extra savings are welcome, of course, but they pale in comparison to the emissions reduction generated by shifting from a private car to a public bus.
If we analyze a whole system instead of an individual, technology’s potential to reduce emissions gains importance, but is still lower than that of modal shift. That means we first need to focus on providing incentives for drivers to leave their cars behind and turn to public transit. When a bus system with exclusive lanes opens, for instance, 1%-5% of passengers are likely to be new riders who used to drive and made a conscious decision to switch. This proportion can increase to 10-15% with the right ancillary interventions, such as providing non-motorized transport infrastructure, improving accessibility and service quality.
Another great source of emission savings is a more efficient system. We have seen reductions of up to 30% in vehicle-kms after a system reorganization. The following graph compares the potential emission reductions of modal shift and fleet rationalization by shifting vehicles to hybrid (left column) or electric (right column) technology.