TORONTO - Ontario's environmental watchdog is recommending a "serious discussion" be held on road tolls to lessen traffic and reduce greenhouse gases.

Environmental commissioner Gord Miller says traffic congestion imposes huge costs on the economy, the environment and public health, and is more than just an inconvenience.

Recent figures from the federal government show Ontario hit its 2014 target for reductions in the gases that contribute to climate change by 2009, at the height of the recession.

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

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

He says the best way for governments to break the link between economic growth and greenhouse gas emissions is to put a price on carbon.