Written by Allen Schaeffer, executive director of the Diesel Technology Forum. This is one in a series of periodic guest columns by industry thought leaders.

Ask the average person on the street what comes to mind when you say the word “diesel.” The majority will respond “truck.” Will it still be that way 10, 20 or even 50 years from now? Yes.

Some are predicting a rise in the use of natural gas engines and even electric motors. Tesla Motors last week said it was moving into the market with an electric semi-truck.

But diesel engines are the overwhelming powertrain of choice for the commercial trucking industry. Because of their transformation to clean diesel technology, gains in efficiency and use of renewable diesel fuels, they will be the dominant player in the future of trucking.

With a fuel that has a 10-percent higher energy density and 20- to 30-percent efficiency advantage over a gasoline engine, more freight and work can be done using a gallon of diesel fuel than other alternatives.

That’s why today more than 95 percent of all heavy-duty trucks are diesel powered, as are a majority of medium-duty trucks. Diesel still offers an unmatched combination of efficiency, power, reliability and durability — attributes that have won truckers over for the last half-century. And the last 15 years have set the stage for the future.

Starting in 2000, a complete transformation of diesel for both on- and off-road applications got underway. The challenge set by the Environmental Protection Agency and the California Air Resources Board was to virtually eliminate emissions of nitrogen oxides and particulate matter from diesel engines by 2010.  Eliminating 97 percent of the sulfur from diesel fuel then enabled the use of new and advanced emissions controls — particulate filters and selective catalytic reduction, or SCR systems — not before seen on diesel engines.

As a result, today’s diesel truck engines are significantly cleaner, reducing emissions by as much as 98 percent from pre-1990 models. To put the progress in perspective, it would take 60 new diesel trucks to equal the same emissions from one pre-1988 truck — a 60-1 ratio!

Beyond the clean-air benefits, model year 2010 and newer clean diesel trucks now achieve 3 percent to 5 percent better fuel economy, which translates into fewer emissions of greenhouse gases, an important new consideration for all fuels and technologies.

The new clean diesel technology is a success story where it matters most — in the marketplace.  Because without truckers embracing technology, there are no fuel savings and no clean-air benefits. Today, more than 40 percent of all medium- and heavy-duty diesel commercial trucks in operation in the United States— 4 million of 9.5 million diesel trucks — are equipped with model year 2007 andnewer technology clean diesel engines. Four states — Indiana, Utah, Oklahoma and Texas — have more than 50 percent newer-generation diesel trucks on the road.

Helping the U.S. achieve its clean-air goals is the underlying reason for the move to clean diesel fuel and engines. Nitrogen oxide, or NOx, emissions from commercial diesel trucks (light-, medium- and heavy-duty) declined by about 60 percent from 2000 to 2015, according to the California Air Resources Board.

More fine particles are emitted from charbroiling a one-third pound hamburger than from driving a new diesel truck 140 miles. In Southern California, more fine particles come from brake dust and tire wear than from heavy-duty diesel trucks.

Getting newer generation trucks on the road is key to achieving clean air and other benefits.

Surprisingly, California — known as a green state — ranks near the bottom of all 50 states in theadoption of cleaner diesel trucks on a percentage basis. There are more than 900,000 Class 3-8 commercial vehicles in California, with about 18 percent being model year 2010 and newer, according to 2015 data. The national average is 26 percent. The reasons for the slower adoption of new diesel trucks in California is probably a combination of factors, including slower demand for freight, economic uncertainties as well as the business and regulatory climate in California. That compares with the strategic permitting, vehicle registration and business operations in other states.

If more of the newest 2010 and later model year clean diesel trucks were on the road, California would go further and faster toward achieving its clean-air and climate change goals.

Efforts by the state to promote alternatives to diesel have delivered only marginal results. Starting in 2007, California began to subsidize commercial truck buyers to purchase heavy-duty natural gas vehicles instead of diesel. At the outset, natural gas trucks were seen as a nascent technology that could reduce emissions, provide clean-air benefits and lower petroleum consumption. Initially, they were able to achieve lower emissions than diesels. But with the advent of clean diesel technology, the emissions are virtually the same for some vehicles.

Since that program began in 2007, $71 million in incentive funding was spent to help purchase 2,826 natural gas commercial vehicles, growing the market to just 1.8 percent of the fleet in almost eight years. And these dollar figures don’t take into consideration the substantial investments for natural gas infrastructure (pipelines and compressor stations), which included another $16 million that California spent to build 51 natural gas stations.

Today in California there are around 15,000 Class 8 heavy-duty trucks running on natural gas and around 900,000 diesel trucks. As a result, the overwhelming majority of the clean-air benefits realized from California’s commercial truck fleet come from adoption of clean diesel trucks, not from natural gas vehicles.

Natural gas works well for some fleets and applications but has not made substantial inroads into trucking because diesel engine emissions and fuel economy improvements are overwhelming motivators for most truck buyers. New engine offerings will increase the appeal, but concerns about methane release causing substantial climate problems and impacts from extracting natural gas are major challenges facing that fuel.

The future is all about improving energy efficiency to lower greenhouse gas and carbon emissions.

Truckers are going to experience this in two ways: the design and performance of future trucks and major changes to make the goods movement and freight system more efficient. This will be accomplished, in part, through greater connectivity in the vehicles and freight system, includingautonomous driving and platooning, which is currently in the testing phase.

New rules for medium- and heavy-duty truck fuel efficiency requirements from EPA, CARB and the National Highway Traffic Safety Administration will be enacted later this year, setting the stage for greater improvements in commercial truck efficiency to lower fuel consumption and achieve reduced CO2 emissions.

Editor’s note: Allen Schaeffer is the executive director of the Diesel Technology Forum, a nonprofit organization dedicated to raising awareness about the importance of diesel engines, fuel and technology.