TORONTO - Ontario must deliver environmentally sustainable transportation to reduce congestion and ease the strain on highways and the environment, the province's transportation minister said Monday.

The population of the Golden Horseshoe, which stretches from Oshawa to Niagara Falls, including the Greater Toronto Area, is expected to grow by 3.8 million over the next 25 years, Donna Cansfield told a sustainable transportation conference in Toronto.

"While the potential positive impact of that growth is enormous, the threat to the environment is serious,'' she said.

That growth could mean a 45-per-cent increase in average commuting time and a 42-per-cent increase in car emissions, she said.

"If we don't deal with this problem today, we'll have a far worse problem tomorrow.''

Calling public transport the "backbone'' of the government's plan, Cansfield said drivers -- especially those who drive alone -- need to be given attractive alternatives to commuting.

Cansfield pointed to GO trains and buses, and high-occupancy vehicle lanes as measures intended to cut congestion.

Gridlock already costs Ontario's economy billions of dollars each year in pollution, lost productivity and delays in the movement of goods, added Cansfield.

"We're dealing with years of underfunding and neglect in the transportation infrastructure in this province,'' she said. "The old way of thinking about transportation was focused too much on roads and highways, not enough on alternatives.''

Last week, the Ontario government vowed to expand the number of HOV lanes on the province's 400-series highways.

A northbound high-occupancy lane on Highway 404 is set to open this summer, with others on it and Highway 400 planned over the next decade.

The HOV lanes, which are restricted to vehicles carrying at least two occupants, first opened on sections of highways 403 and 404 in December 2005. Motorists without passengers who are caught using the lanes face fines of $110 and three demerit points.