Global demand for cars is likely to continue its upward trend when economies improve. This will put more pressure on oil resources and the environment as the era of plentiful oil comes to an end and emissions from autos contribute to global warming. Today’s transportation systems are unsustainable in the long run unless vehicles are adapted to run on either electricity or biofuels. Patterns of urban development and lifestyles also may have to change.

Washington — When asked if gasoline-electric hybrid and plug-in hybrid vehicles are the most promising auto technologies, Rob Farrington paused. It wasn’t that he did not know the answer. After all, he heads the advanced vehicle group at the National Renewable Energy Laboratory in Golden, Colorado. It was that the question did not address the real issue.

“The most promising solution to our dependence on imported oil and the climate change challenge is to get people to use transportation other than individual vehicles,” he said.

Like bicycles?

Yes, biking, hiking, ride sharing and telecommuting are all part of the solution.

“These are the things we have infrastructure for and there is no additional cost involved,” he said.

But above all, he meant public transport.

“It’s not a tech solution, so it is not fashionable,” he said. “But the sooner we consider it seriously, the better.”

Most experts believe that a mix of advanced automotive technologies, better public transport and other alternatives to individual driving will be needed to reach the ambitious goals set by President Obama for 2020: 14 percent cut in U.S. greenhouse gas emissions below 2005 levels and 1.8 billion barrels of petroleum saved through vehicle fuel efficiency. Passenger vehicles and light trucks account for almost 45 percent of U.S. petroleum demand and 17 percent of greenhouse gas emissions, which contribute to global warming.

Making public transport a viable alternative to car commuting will require many infrastructure investments. Congress is likely to significantly increase funds for public transport infrastructure when it considers a transportation bill later this year. But transportation projects take considerable time to complete.

Plug-in electric hybrid technology, about which the president is particularly enthusiastic, is unlikely to make a significant impact on the market in the next few decades, according to analysts, despite a call from the White House to put a million such vehicles on the road by 2015.

Farrington said it would take 15 years to replace the entire U.S. passenger auto fleet if every vehicle sold today were a hybrid or plug-in hybrid. Hybrids have been on the market for almost 10 years but make up only 3 percent of new vehicles sold today. What’s more, their producers have yet to make profits on them, according to Dave McCurdy, president of the Alliance of Automobile Manufacturers.

To maximize fuel savings and emission reductions in the shortest period, the focus should be on improving conventional gasoline-fueled internal-combustion vehicles and discouraging individual driving, experts say.

Policymakers, however, prefer to talk about the “transformation” of transportation and “transformative” technologies, according to John Heywood of the Massachusetts Institute of Technology, who has researched vehicle technologies.

“For politicians, ‘improving’ [vehicles] and ‘conserving’ [fuel] do not create the same sense of excitement as ‘transformation,’” he said.

Most analysts agree that research on advanced auto technologies should accelerate, and they praise the administration for putting up considerable funds for it. But Farrington cautioned against a singular focus on technology, which he said does not encourage the necessary cultural shift toward heavier reliance on public transport and more compact, walkable communities built around mass-transit hubs.

Part of the problem is the lack of comprehensive and consistent national energy and transportation strategies, McCurdy said at a June 18 public meeting.

At an earlier June meeting, Beth Osborne, deputy assistant secretary of transportation, said the administration works aggressively to come up with such strategies. But it faces a formidable task of breaking through bureaucratic walls separating different agencies, which have powers over different aspects of related issues, she said.

Efforts to come up with such strategies are further complicated by the fact that the goals of increasing energy security and decreasing global warming are not always compatible. For example, the United States can expand a range of secure sources of fuels by encouraging production of heavy oils on its own soil and in Canada, thus increasing energy security. But such production is energy-intensive and causes environmental damage.

Just a few years ago, biofuels, primarily ethanol, were viewed as a solution to both U.S. energy and climate problems. In 2007, Congress — motivated by security concerns — mandated a fivefold increase in their production. Now Congress is considering a bill that would require at least 80 percent of new automobiles to be able to operate on biodiesel or ethanol and methanol blends by 2015. Automakers have pledged that half of all vehicles produced by 2013 will have that capability.

But a number of studies have cast doubt on net climate benefits of biofuels, primarily corn-based ethanol.

Those studies “got us more cautious,” Heywood said.

That is why he and Farrington recommend “very aggressive” development of the next generation of biofuels — based on cellulosic biomass — whose climate benefits are expected to be more obvious.