What’s holding up progress on alternative fuels? Despite all the publicity and development of new products from truck and equipment manufacturers, especially for natural gas, trucks that run on gases and liquids other than diesel and gasoline are still a small minority of all those being bought in recent years, acknowledged panelists at the Alternative Clean Transportation Expo, which runs this week in Washington, D.C.

The panelists at the meeting’s first “plenary” session head advocacy groups promoting natural gas, propane, electric propulsion and clean diesel. Though there’s been competition for attention and financial backing among them, Tuesday’s session showed far more agreement than anything. And most said they’d like to see things move faster.

They cited a number of reasons for the inertia in adoption of alternative fuels:

• Inconsistent public policy as set by Congress, which has established tax credits and monetary grants, then let them expire, then re-establish them. Fleet managers need steadier signals on which to base business decisions.

• Lack of infrastructure to support natural gas fueling, although progress is being made.

• High cost of storage tanks at fueling stations and aboard trucks.

• Bankruptcies among battery and electric-vehicle suppliers.

• Success of ultra-low-sulfur diesel fuel and the engines that burn it, so diesels are still the most popular heavy and medium-duty engines by far.

The last point was made by Allen Schaefer of the Diesel Technology Forum, which represents engine and truck builders. Diesel fuel continues to have the highest energy density available, and the alternatives, while cheaper, continue to be measured in diesel-equivalent terms. Diesel fueling stations are almost everywhere and remain relatively inexpensive to set up and maintain.

And, Schaeffer said, nearly 30% of diesels on the road were built in 2007 or later, making them clean burning and environmentally friendly. Biodiesel blends are becoming more important, giving the fuel a touch of sustainability.

Nonetheless, there is momentum for natural gas, both compressed and liquefied, said Marty Durbin of America’s Natural Gas Alliance. He quoted a prediction that 30% of new trucks will be natural-gas-fueled by 2020. Some fellow panelists thought that might be optimistic.

As he has at other meetings, Ray Willis of the Propane Education Council called attention to propane “autogas,” the most popular alternative fuel in the world, except in North America. But fleet managers are finding out about its clean-burning characteristics and inexpensive pricing – roughly the same as natural gas. Handling and storage are also inexpensive and fueling stations cost a fraction of those for natural gas.