Pictured from left to right: Tom Stricker, Toyota; Robert Bienenfeld, Honda; Reg Modlin, Chrysler.

Now that car buyers are starting to accept hybrids and EVs, there's more willingness to consider other green car technologies, including diesel, CNG and hydrogen. But the road to wider acceptance – and affordability – is being slowed by a lack of infrastructure and overlapping state and federal regulations that are sometime are at odds with one another.

That's the view of environmental and regulatory experts from three automakers, Toyota, Honda and Chrysler, who spoke speaking to an audience of journalists and policy-makers at the opening of 2013 Washington Auto Show, now underway.

Chrysler's head of regulatory affairs, Reg Modlin, said he is optimistic that investment by corporate fleets in CNG and electric will drive (pardon the pun) infrastructure development, citing that 20 states now are pushing CNG fleets. "The government has a role, but the marketplace has a bigger one," he said.

Robert Bienenfeld, Honda's manager of environment and energy strategy, is hopeful that the network of 100 hydrogen fueling stations California is planning to will "send a strong signal" for the viability of fuel cell vehicles, first for fleets, then for consumers. Honda's FCX Clarity fuel cell sedan has been leased in California for several years already.

What about renaming the technology as "natural gas fuel cells" to bypass consumer reluctance to hydrogen?

Toyota's VP of energy and environment research, Tom Stricker, predicts more collaboration between competing automakers to reduce R&D costs, such as Toyota's partnership with BMW on fuel cell research. He even suggested using natural gas to make hydrogen, and renaming the technology as "natural gas fuel cells" to bypass consumer reluctance to hydrogen.

All three agree that oil companies should ramp up production of low-sulfur fuel. "Direct injection engines need it to live," said Chysler's Modlin. Having one national standard for Tier 3 fuel will help lower prices nationwide, said Honda's Bienenfeld, adding, "if you don't have consumer support, you can't have policy." All three are optimistic that EPA fuel economy standards for 2025 will be met, although Striker describes the rules as "not really about fuel economy, but about CO2 reduction."

Honda's Bienenfeld noted that 40 years ago, cars were "1,000 times more polluting and half as fuel efficient." He predicts engines will continue to get cleaner and more fuel efficient, further narrowing the gap between conventional powertrains, including diesel and hybrids.