Truckmakers Navistar, Daimler, Volvo and others, along with engine-maker Cummins, are placing bets on various forms of new technology in a drive to boost fuel efficiency and cut down on emissions.

Truck and engine manufacturers are tinkering with new engines, trailer designs and other innovations. Some want to break completely from the combustion engine and develop fleets of fully electric trucks, several prototypes of which are being road-tested. Others are trying to improve the efficiency and emissions output of diesel-fueled vehicles.

Agility has invested in Hyliion, a retrofit add-on that involves installation of an intelligent drive axle on a trailer. The system, installed in 60 minutes, uses regenerative braking to capture and save power when the truck is slowing, then reuses that energy to provide power when the truck is climbing hills. Depending on the topography and normal fuel economy of the vehicle, the Hyliion system can reduce fuel use by 30 percent and cost by $1,300 a month.

There are 1.7 million tractor-trailer trucks in the United States alone. The average heavy-duty truck gets only six to seven miles to the gallon. Some estimate that an extra mile per gallon would be the equivalent of removing 200,000 of those trucks from the road each year.