An energy transition is underway. Solar and wind are being added in ever-greater numbers. Electric vehicles are becoming more commonplace. Meanwhile, policy makers are grappling with the right mix of policies to pay for it all.

Elon Musk knows how to make promises. Even by his own standards, the promises made last week while introducing two new Tesla vehicles—the heavy-duty Semi Truck and the speedy Roadster—are monuments of envelope pushing. To deliver, according to close observers of battery technology, Tesla would have to far exceed what is currently thought possible.

When Nikola Motor Co. President Trevor Milton pulled the wraps off the Nikola One prototype Class 8 truck last year and announced it would have a hydrogen fuel-cell power plant, it seemed a radical approach at the time.

Video: Cummins' Tim Proctor, left, talks with TT's Roger Gilroy about meeting the fuel economy needs of customers who are concerned about global warming.

HAWTHORNE, Calif. — Tesla’s success in the passenger-car arena has changed consumers’ perceptions and pushed the limits of what’s possible with electric cars.

Frito-Lay Senior Director of Supply Chain Mike O'Connell, right, discusses PepsiCo's "Performance With Purpose" strategy to reduce the greenhouse gas impact of its fleet with TT's Roger Gilroy.

North American Council for Freight Efficiency Executive Director Mike Roeth (right) discusses diesel efficiencies demonstrated during the Run on Less event, and where diesel fits into the future of trucking as a power source, with TT Executive Editor Joe Howard.

"Natural gas is ready right now, it’s available, and it should be part of that overall equation when any fleet operator or transit company looks to deliver goods," says Dan Gage (right), president of Natural Gas Vehicles for America, talking with TT's Joe Howard. More at bit.ly/TT-LOW1117. (Joseph Terry/Transport Topics)

Customers are starting to place orders for Tesla Inc.’s new all-electric Semi truck, with retail giant Wal-Mart Stores Inc. preordering for both its U.S. and Canadian units.