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Speed Kills Hybrid and Plug-in Vehicle Savings, CMU Researchers Report
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June 18, 2013

Speed Kills Hybrid and Plug-in Vehicle Savings, CMU Researchers Report

By Cheryl Kaften
TMCnet Contributor

The “mean streets” of America’s cities are actually more sympathetic to hybrid and plug-in vehicles than superhighways, according to the latest research news out of Pittsburgh-based Carnegie Mellon University (CMU).  

Interestingly enough, the study also found that aggressive operation of a vehicle on a highway  can cost more to the driver and the environment than following the rules of the road.

Recently, 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 hybrid and plug-in vehicles cost […] more when driven on highways—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, just as the Environmental Protection Agency (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 explained. "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 the research team. "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," the authors said.

Michalek advises, "The bottom line is: before you buy, consider how you drive."

Edited by Blaise McNamee

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