Several hundred opponents of a contentious plan to increase diesel passenger train service through central Toronto gathered Saturday to protest what they say is an unhealthy decision that will pollute the air in their neighbourhood.

The demonstration was spearheaded by the Clean Train Coalition, which is attempting to block a proposal that could result in about 400 daily diesel train trips through western sections of the city.

Metrolinx, the regional transit authority which has replaced GO Transit, hopes to use diesel trains on the Georgetown south corridor, which would link Brampton and Pearson International Airport with Union Station.

But residents along the train corridor, in neighbourhoods like Weston and The Junction, say that hundreds of daily diesel train trips will create health problems and bad air.

Instead, they are asking that Metrolinx devise a plan to use electric trains.

The protestors gathered at Sorauren Park around 2:30 p.m. in Roncesvalles Village after creating a "human train" that walked along the proposed corridor.

Among the demonstrators was Liberal MP Gerard Kennedy (Parkdale - High Park) and Dr. David McKeown, who is Toronto's Medical Officer of Health. McKeown has been vocal about the plan in the past.

"What we know about air pollution in Toronto is that any proposal now should pass a very stringent test before it goes forward," McKeown stated in a media release authored by the Clean Train Coalition.

"This proposal has not passed that test in my view," he added. "The study, conducted by Metrolinx itself, indicates clearly that there will be impacts on air quality as well as health risks for those that live close to the line."

Metrolinx has said that the system will be able to operate "safely without posing a risk to human health on most days." However, it has said that on bad smog days, it will use a "mitigation plan" to limit harmful exhaust.

The transit authority has estimated that electrifying the Georgetown line would cost about $1.5 billion, and Metrolinx is currently conducting a study to weigh the benefits of switching over the entire GO system. The study is expected to take about 14 months.

Meanwhile, Metrolinx has pledged that it will use the greenest diesel fuels available.

Meanwhile, Kenney welcomed the electricity study.

"I know that the people in this community want decent public transit everywhere. Metrolinx has breached the trust of this community," said Kennedy in a statement released after the march.

He added that using electric trains should be seriously investigated, even if it delays the project.

"If (Metrolinx) says it takes a year to do a study for electric trains, then nothing should happen here for a year. This requires us to not put up with what Metrolinx has been doing in Toronto."