Ontario's environmental watchdog is calling for a "serious discussion" on road tolls to decrease traffic and reduce greenhouse gases, but all three major parties say if they are elected this fall they don't plan to make motorists pay to use roads.

Transportation accounts for the largest volume of greenhouse gas emissions in the province -- about 34 per cent -- with most coming from personal vehicles, according to a new report released Tuesday.

"Not only are we failing to aggressively address reductions in this sector but the government has actually terminated three of the GHG reduction programs that were operating in that sector," said environmental commissioner Gord Miller.

Gridlock is more than an inconvenience -- it imposes huge costs on the economy, the environment and public health, he said. And you don't need to go far in the Greater Toronto area to see how road tolls can reduce congestion.

"We have two major highways that go east-west across the city: one is the 401 and one is the 407," he said. "And most mornings, at about 8 o'clock in the morning, one is not moving very fast and the other is moving quite smoothly -- and one has a toll on it."

Miller acknowledged road tolls may be politically unpalatable, particularly when Ontario voters will be heading to the polls Oct. 6.

All three major parties did little to dispel that notion by quickly shooting down the idea.

"We're not looking at road tolls," said Transportation Minister Kathleen Wynne. "The decision we made was that we were going to take money from the gas tax and we were going to put that into transit building -- that's what we've done. So $320 million or so a year goes into transit around the province and we're going to continue with that funding."

Both the Progressive Conservatives -- who created the 407 toll highway -- and New Democrats also steered clear of the potentially radioactive issue, saying they'd find other ways to reduce congestion and greenhouse gas emissions.

There would be no new road tolls under a Tory government, said Opposition Leader Tim Hudak. Instead, the party would invest $35 billion in infrastructure over three years, much of it in transit and transportation.

"I'm a young dad, I get stuck in traffic too," Hudak said. "I feel it. I mean, you're stuck in traffic -- that's time taken away from my wife Debbie, my daughter Miller. I want to make sure we get families closer to home as fast as possible."

Right-leaning Toronto Mayor Rob Ford has also ruled out tolls to pay for a $4.2-billion expansion of the Sheppard subway line, after the man he hired to find funding, Gordon Chong, raised the idea.

But Ontario needs to find a way to put a price on carbon like British Columbia, Alberta and Quebec have, Miller said after delivering his annual report on the province's progress in reducing emissions.

He said he's disappointed the Ontario government recently announced a delay in participating in a regional cap-and-trade system for carbon.

The best way for governments to break the link between economic growth and emissions is to put a price on carbon, he said.

Recent figures from the federal government show Ontario hit its 2014 target for greenhouse gas reductions by 2009 -- when the province was in the throes of a recession that shut many plants and factories, his report said.

However, it's "highly likely" that emissions have increased in the past two years with the return of economic growth as manufacturing facilities fired back up, Miller added.

So far, only the Green party has promised to bring in a carbon tax if they win the Oct. 6 election. The Liberals, Tories and NDP have all ruled it out.