A new report suggests light rail transit is Toronto's "greenest" travel option, claiming the city should stick to its current Transit City plan to link the suburbs with downtown.

The report, released by the Toronto Environmental Alliance (TEA), appeals to Toronto's newly elected City Council to consider the environmental impact of their future transit plans.

While the current Transit City growth strategy calls for an expansion based primarily on streetcar routes and light rail, Mayor-elect Rob Ford made his promise to expand subway lines a central part of his election campaign.

"As the new City Council discusses how to get fast, reliable public transit into Toronto's inner suburbs, it needs to consider the environmental impacts of the various options," Dr. Franz Hartmann, TEA's executive, said in a statement. "The facts suggest that Light Rail Vehicles, not subways, are the best technology –per dollar invested- to reduce greenhouse gas emissions."

The report titled Clearing the Air on the TTC, takes direct aim at comparing subways and light rail, calling subways the preferred option in "a world where tax dollars were not scarce, where there was lots of time to plan and build transit, where traffic congestion was a minor irritant, and where climate change was not a global threat."

The study suggested diesel buses emitted 116.6 tonnes of greenhouse gas for every kilometre traveled by one million passengers.

Light rail vehicles emitted 39 tonnes compared to the same benchmark, while subways emitted 29 tonnes. It noted that subways cost three to five times the amount of light rail, making them less attractive when cost is factored in.

"It's clear that from an environmental perspective, the 2007 Transit City Plan is the best plan," Hartmann said. "I hope this new information will help convince City Council that subways are not the answer to getting fast, reliable transit to all four corners of the City. Rather, City Council should go with the option that is best for the environment and the pocketbook: Transit City."

The report, which was co-authored by a new advocacy group called TTCriders, said the current transit system stops Torontonians from burning the equivalent of 140 million litres of gas each year.