WASHINGTON  Fri Jan 16, 2015 6:56pm GMT

Current low oil prices are a short-term blip and will not affect how the U.S. crafts new environmental regulations, including forthcoming standards for heavy duty vehicles, the Environmental Protection Agency (EPA) chief said Friday.

EPA Administrator Gina McCarthy said the agency's next move to tackle greenhouse gas emissions will come this spring when it unveils new fuel efficiency standards for commercial vehicles - the second biggest source of domestic transportation emissions.

Although crude oil prices have fallen almost 60 percent over the last six months with both of the world's crude oil benchmarks now trading below $50 a barrel, McCarthy said consumers will continue to favor more fuel efficient cars and trucks and car companies will continue to design them.

"Even though you see that the gas price has gone down, I see no indication long term that people are changing their buying habits," McCarthy told reporters at a briefing at her office.

"We don't think that this small timeline, where there is this extreme fluctuation, is going to continue," she said.

The EPA is working on the next round of fuel standards for trucks that will extend beyond current rules for the 2014 to 2018 period.

The rules will cover large tractor trailers, trucks and other commercial vehicles.

"It's extremely important to recognize that goods movement in this country relies considerably on these vehicles and these vehicles last for upwards of a million miles," McCarthy said. "This is a big deal for us."

McCarthy said the agency has been working closely with the auto industry and the Department of Transportation on the next round of rules.

McCarthy on Friday also addressed concerns raised by some environmental groups that the agency's new proposal to curb methane emissions from oil and gas production relies heavily on voluntary industry measures and doesn't tackle existing sources of emissions.

The White House proposed on Wednesday to slash methane emissions from oil and gas by 40 to 45 percent from 2012 levels by 2025 through a hybrid of mandatory rules tackling new facilities and voluntary programs for industry.

She said the mix of mandatory and voluntary measures will send a strong signal to industry and investors about opportunities to tackle methane leaking from oil and gas infrastructure.

"People shouldn't think the only thing to expect is those emissions to increase. You will see emissions from existing facilities continue to increase as a result," she said.