The Ontario Ministry of Environment has approved a contentious proposal to allow hundreds of new diesel trains to pass through some neighbourhoods in west end Toronto.

Metrolinx — the regional transit agency formerly known as the Greater Toronto Transit Authority — wants to expand the GO Transit line's south Georgetown corridor to link Union Station and Pearson International Airport.

When the expanded line begins operation in 2015, total traffic on the Georgetown corridor is expected to increase to more than 400 diesel trains a day from about 50.

Community groups have opposed the proposal, saying emissions from the diesel trains would hurt the health of thousands of people who live in the area around the tracks. The tracks run through parts of Parkdale, the Junction and north past Weston Road toward Brampton.

The Ministry of Environment, in part to assuage health concerns, has drawn up a list of conditions that Metrolinx has to meet when constructing the expansion. Some of these conditions are:

• Trains must use new low-sulphur diesel engines that emit 90 per cent fewer particles and 80 per cent fewer nitrous oxides than traditional engines.
• Metrolinx must conduct further studies on air quality and work to mitigate potential risk factors as they arise.
• The agency has to consult with people who live along the tracks on its plan to monitor air quality and minimize risk factors.

But many community groups oppose diesel trains outright and have said any new trains must be electric.

The Clean Train Coalition has organized a number of protests against the proposal, most recently a rally on Saturday that drew hundreds of protesters in Parkdale.

Electrification too expensive, says Metrolinx

Metrolinx has said electric trains are an option down the road. But the estimated $1.5-billion cost to electrify the line is too expensive to implement immediately, the agency said.

Toronto's chief medical officer of health, Dr. David McKeown, has also said that the new trains could impact public health. He wrote to the Ministry of the Environment to say he is worried the expansion could cause air quality issues.

Diesel exhaust has been identified as a probable human carcinogen by several agencies, including the International agency for Research on Cancer.

Metrolinx, however, has said there is no increased risk of cancer for people living near the tracks.