Metrolinx hopes to eventually electrify a GO Transit Rail Link between Toronto's Union Station and Pearson International Airport. (Canadian Press)

Provincial transit agency Metrolinx is recommending the controversial rail link from downtown Toronto to Pearson airport be electrified eventually, but only after diesel trains first run on the line when it opens in 2015.

Metrolinx on Wednesday released a staff report that called for the eventual electrification of GO Transit's new Airport Rail Link (ARL), along with the existing Georgetown and Lakeshore lines. The report says converting diesel trains on those three lines to electric ones will cost between $1.6 and $1.8 billion, a bill that will likely have to be picked up by the province.

The ARL, an express commuter line that is currently under construction, will link Toronto's Union Station to Pearson Airport. The air link would be the first of the three lines to be electrified, although that will not happen in time for the 2015 Pan Am Games under the Metrolinx proposal.

Rather, the first trains to run on the link will be diesel Tier 4 trains, which Metrolinx says produce fewer emissions than traditional diesel trains. The electrification of the corridor would take place after that, the report says.

Electrification on that stretch could take anywhere between seven and 10 years and would cost $457 million, Metrolinx said.

The report, which will be presented to Metrolinx's board on Jan. 26, acknowledges that a "risk mitigation plan" needs to be developed to address challenges like a "lack of sustained funding" for the electrification proposal.

Originally, Metrolinx had committed only to having diesel trains operate on the airport link and the expansion of GO's Georgetown line. But community advocates in west Toronto voiced strong opposition to that move, saying that emissions released by the diesel trains would pose a health risk to those living on or around the line.

The recommendation to electrify the lines comes after the agency conducted a yearlong study that assessed the environmental and financial impact of electrification. The study found that electrifying rail lines does not "significantly" reduce greenhouse gas emissions. But the report concluded that electric locomotives can save passengers on average between 2.4 and 2.8 minutes per trip.

Electrifying the Lakeshore and Georgetown lines provides the greatest bang for the buck because they have the highest ridership, the report found. Both those lines are currently undergoing $2 billion in service expansion.

The report also found that electrifying the lines in question could save up to $18 million annually in operating costs, due to the cheaper cost of electricity and the need for fewer parts to maintain.