The dip in oil prices is temporary and will not affect the way federal agencies set fuel economy standards, including upcoming new requirements for heavy trucks, said EPA Administrator Gina McCarthy.

McCarthy told reporters that despite a near 60% drop in fuel prices over the last six months, car and truck buyers will continue to favor more fuel efficiency, according to a Reuters account.

The Environmental Protection Agency and the National Highway Traffic Safety Administration are working on the next phase of medium- and heavy-duty fuel economy standards. The proposed rule is due in March, with the final rule to follow in March 2016.

McCarthy said the standards are a “big deal” because freight movement relies on heavy trucks that are in service for close to a million miles, Reuters reported.

She also said she does not expect fuel prices to stay as low as they are.

The first round of greenhouse gas emission rules for trucks, posted in 2011, set standards for model years 2014 through 2018. It focused on efficiencies obtained by refinements to tractors and engines. This next round will be more ambitious.

EPA and NHTSA will assess trailer aerodynamics as well as engine and powertrain improvements, weight reduction, improved tires, automatic engine shutdown and accessories such as water pumps and fans. They also will look at hybrid technologies.