Toronto will have to make great strides to reach its target of net zero emissions by 2040, including transitioning every single gas-guzzling vehicle in the city's inventory.

That plan includes the ongoing replacement of the TTC's vast bus fleet in a process that involves swapping out hundreds of fuel-burning vehicles for hybrid-electric buses.

The TTC announced on Wednesday that it had begun to receive the first vehicles in an order of 336 additional hybrid-electric buses inked in early 2022 for delivery this year. Passengers will be riding the first of these new additions to the fleet in May after inspection and testing is complete.

Passengers looking to test out the new buses for themselves will be able to board these updated additions to the fleet in the TTC's Mount Dennis and Wilson divisions, serving routes in midtown, downtown, North York, and Etobicoke.

🎉Exciting news! Our new hybrid-electric buses are launching in May. They'll replace older models, reduce greenhouse gas emissions & improve air quality.

By mid-2024, one-third of our bus fleet will be low or zero emissions.🌿 https://t.co/NSHW5KpIjT pic.twitter.com/1ZFyJr1vFa

— TTC Customer Service (@TTChelps) April 19, 2023

New buses will replace existing vehicles deemed to have reached the end of their useful service life. Though the size of the fleet will not increase through these replacement buses, larger vehicles mean more capacity for the transit agency.

One example is the introduction of 68 new sixty-foot hybrid-electric buses that will replace the same number of older forty-foot buses. At an extra 20 feet of length per bus, the 1,360 feet of added bus length is equivalent to adding 34 extra buses to the fleet.

In addition to these 60-foot models, the TTC is also introducing 134 forty-foot hybrid-electric buses manufactured by Nova, and another 134 built by New Flyer.

"Hybrid-electric buses offer residents and visitors a clean, quiet, and healthy alternative to travel around our city," said Deputy Mayor Jennifer McKelvie.

"These new buses demonstrate the City of Toronto's continued efforts to reduce our cumulative carbon footprint, shape a sustainable city, and achieve our goal of net zero emissions by 2040."

This hybrid technology, while a huge improvement over earlier fossil-fuel-exclusive buses, is still only an intermediate step to full electric for the TTC.

In a press release announcing the delivery of the new buses, the TTC states that "the only distinction between a hybrid and an eBus is that the hybrid has an onboard generator that produces electricity when needed."

It's a sort of band-aid solution that the TTC will only pursue in the interim, and 2024 will mark the final year the transit agency takes on low-emissions vehicles. After 2024, the TTC will exclusively purchase all-electric buses in its final 15-year push to reach net-zero emissions.

The transit agency expects one-third of its fleet to reach low- or zero-emissions status by next year.

"The TTC is committed to being completely zero-emissions by 2040 or sooner," said TTC CEO Rick Leary.

"As eBus technology is still developing, we've purchased hybrid-electric buses, which are a proven transition technology. With the addition of these new, modern vehicles to our fleet, we are well on our way to achieving our goals while continuing to focus on delivering reliable service."