Do Hybrids Save Money? Depends How You Drive

Vehicle window stickers, fuel economy standards and even life cycle studies offer incomplete efficiency estimates for vehicles because they often fail to account for driving conditions, a Carnegie Mellon University analysis has found. Researchers concluded that driving patterns have a substantial effect on the economic and environmental benefits of electric vehicles.

CMU researchers Orkun Karabasoglua and Jeremy Michalek compared hybrid, extended-range plug-in hybrid and battery electric vehicles for their potential to reduce lifetime cost and life cycle greenhouse gas emissions under various scenarios and simulated driving conditions with findings including:

• Drivers who travel in New York City-style conditions could cut lifetime costs by up to 20 percent by selecting hybrid vehicles instead of conventional vehicles;
• Under the NYC driving condition, hybrid and plug-in vehicles can cut life cycle emissions by 60 percent and reduce costs up to 20 percent relative to CVs;
• Under HWFET conditions – or highway test driving under 60mph – drivers of conventional vehicles see a lower lifetime cost option without a major GHG emissions penalty;
• Under HWFET conditions hybrid and plug-in vehicles offer few GHG reductions, at higher costs.
• Under US06, an aggressive driving style characterized by high acceleration, the all-electric range (AER) of plug-in vehicles drops by up to 45 percent compared to milder test cycles like HWFET, CMU said.

The study, "Influence of Driving Patterns on Life Cycle Cost and Emissions of Hybrid and Plug-in Electric Vehicle Powertrains," comes as the EPA has planned new fuel economy labels starting with 2013 vehicles. These labels give consumers information about performance, e.g., the vehicle's AER, fuel economy, estimated annual fuel cost, emissions, and smog rating. The new fuel economy labels will give information for consumers to make purchase decisions by providing a common ground, but the labels are lacking the critical comparison data about driving conditions, the report said.

The report acknowledges that most consumers are aware of differences between vehicle stickers and their own driving results. However, the introduction of hybrid and plug-in powertrains increases the significance of aggressive and stop-and-go driving conditions on the system efficiency – because of regenerative braking and engine idling. This leads to an increase in the importance of matching the right vehicle to the right driving conditions in order to meet vehicle efficiency expectations, the researchers said.

Picture credit: EPA