Toyota Prius V

OK, maybe this newsflash is an obvious one to longtime green-car observers, but the folks at Pittsburgh's Carnegie Mellon found it worth publicizing that hybrids are a lot more useful to city drivers than highway hounds.

Heavy-footed driving may reduce all-electric vehicle range by as much as 40 percent.

In short, the payback for the additional acquisition cost usually associated with hybrids will take a lot longer for people who do a lot of highway driving than for those staying within the city limits and who do a lot of stopping and going. In fact, for city drivers, lifetime costs for a hybrid may be 20 percent lower than for conventional vehicles, while emissions may be cut by as much as 50 percent. Of course, big hybrid sellers Toyota and Ford helped fund the Carnegie Mellon study, along with the National Science Foundation.

Additionally, and perhaps more importantly, the report found that heavy-footed driving may reduce all-electric vehicle range by as much as 40 percent.

Unlike conventional cars, which often get fuel economy ratings that are 20 percent to 30 percent higher on the highway than in the city, hybrids see little if any fuel economy gains on the highway. For instance, the standard Toyota Prius has an EPA-rated 51 mpg city rating and a 48 mpg highway rating, while the Ford C-Max Hybrid has identical 47 mpg ratings for both city and highway driving.

Check out Carnegie Mellon's press release below. It doesn't mention diesel vehicles, but we're guessing most readers know that they're the ones that prefer to be on the highway. Figuring out the best powertrain for you really is a function of where you spend most of your driving time.
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Carnegie Mellon Researchers Report Hybrid Cars Are Greener for City Drivers

PITTSBURGH, June 17, 2013 /PRNewswire/ -- Will that hybrid vehicle pay for itself and help the environment? That depends on how and where you drive, Carnegie Mellon University researchers report.

Jeremy Michalek, a professor of mechanical engineering and engineering and public policy at CMU, and Orkun Karabasoglua, a mechanical engineering research assistant, analyzed the potential cost and greenhouse gas savings of hybrid and electric vehicles under different driving conditions.

"We found that for highway drivers, hybrid and plug-in vehicles cost more without much benefit to the environment," Michalek said. "But for drivers who experience a lot of idling and stop-and-go traffic, a hybrid could lower lifetime costs by 20 percent and cut greenhouse gas emissions in half."

The study, funded by the National Science Foundation, Ford and Toyota, appears in the journal Energy Policy as the EPA is rolling out new fuel economy labels starting with 2013 vehicles.

"The new labels are improved, but no single test can capture all kinds of driving," Michalek said. "Hybrid and plug-in vehicles will do the most good at the lowest cost if adopted by drivers who spend a lot of time in traffic. For these drivers, hybrids are a win-win, and the benefits may be much more than the labels suggest."

The U.S. government uses standard laboratory tests to measure vehicle fuel efficiency for federal fuel economy labels and standards.

"The fuel economy standards are still based on old lab tests that make vehicles appear to be more efficient than they really are," Michalek said. "This has always been an issue, but it is simplified with today's vehicle technologies. These tests may be underestimating the relative real-world benefits of hybrid and plug-in vehicles."

Driving conditions affect not only cost and emissions, according to Michalek. "Aggressive driving can cut vehicle range by 40 percent or more. That's a notable risk for pure electric vehicles, which already have limited range and take a long time to recharge. But with hybrid electric vehicles, which run on gasoline, and plug-in hybrid electric vehicles that use electricity for short trips and switch to gasoline for longer trips, there's no added risk of being stranded," he said.

Michalek reports that "the bottom line is: before you buy, consider how you drive."

About Carnegie Mellon University: Carnegie Mellon (www.cmu.edu) is a private, internationally ranked research university with programs in areas ranging from science, technology and business, to public policy, the humanities and the arts. More than 12,000 students in the university's seven schools and colleges benefit from a small student-to-faculty ratio and an education characterized by its focus on creating and implementing solutions for real problems, interdisciplinary collaboration and innovation. A global university, Carnegie Mellon's main campus in the United States is in Pittsburgh, Pa. It has campuses in California's Silicon Valley and Qatar, and programs in Africa, Asia, Australia, Europe and Mexico. The university has exceeded its $1 billion fundraising campaign, titled "Inspire Innovation: The Campaign for Carnegie Mellon University," which aims to build its endowment, support faculty, students and innovative research, and enhance the physical campus with equipment and facility improvements. The campaign closes June 30, 2013.