With the last stage in emission regulations for commercial vehicles now complete, truck OEMs and engine makers are turning their engineering sights back on a familiar topic: improving fuel economy.

“Over the last decade, especially in the on-highway truck market, it’s been all about who can meet emission [rules] best,” said Richard Freeland, the new president of Cummins Inc.’s truck engine division, during a news conference at last week’s Mid America Trucking Show.

“But I think as you look out over the next decade, it’s all about fuel economy,” he continued. “I think that’s the new battleground; who can deliver the best fuel economy.”

As a result, heavy-duty fleets will see and hear more about a variety of fuel-saving technologies, Freeland said, including hybrids, waste-heat recovery, high-efficiency aftertreatment systems, high- efficiency turbochargers, etc.

“We’re all in a race again,” he said. “From the standpoint where we [as manufacturers] kept bringing out new products to meet emission targets, now we’ll be aggressively focusing on fuel economy.”

That race is already on fast and furious in the highway tractor segment, with Peterbilt Motors Co. Kenworth Truck Co., and Navistar all rolling out new models or upgrades designed to boost fuel efficiency.

For its new Model 587, Peterbilt’s engineers decreased aerodynamic drag by 2.5% due to a new streamlined hood design and molded bumper, resulting in a 1.25% fuel efficiency gain, said Landon Sproull, the OEM’s chief engineer. (See video of the Model 587)

Kenworth boasts that its sleek new T700 highway tractor cuts drag by 3% compared to its T660 highway model, resulting in 1.5% more fuel efficiency. “The T700 has the lowest aerodynamic drag of any truck in our history,” said chief engineer Preston Feight. (See video of the T700)

Navistar has rolled out an updated version of its ProStar Class 8 model-- the ProStar+-- which features a bevy of new aerodynamic enhancements, including optional full-length chassis skirts for sleepers as well as a new cab-roof air fairing for day cab models.

The ProStar+ also includes new powertrain features that improve fuel economy as well, noted Jim Hebe, senior vp of North America sales operations, including a clutched air compressor, variable speed fan, low-viscosity engine oil and fuel-efficient rear axle lubricant.

“As vehicle weight continues to be a top priority for customers, the ProStar+ is 700 lbs lighter than its predecessor,” he noted during a news conference at the Mid America show.

“Now that compliance with EPA 2010 emission rules is behind us, we have an opportunity to focus on finding more fuel savings for our customers,” Ramin Younessi, Navistar’s group vp of product development & strategy, told FleetOwner at the show.

“In the past several years, 60% to 70% of our R&D budget was spent on emissions,” he explained. “Now we can turn all of that on fuel efficiency. By 2011, we’ll be looking at even more advanced aerodynamics-- not only around the truck. but through the engine and under it as well, managing the tractor/trailer gap, and figuring out how to remove more ‘parasitic’ loads from the engine.”