Researchers Detail How Driving Conditions Affect EV Range

The all-electric range of a plug-in hybrid can drop as much as 45% when the vehicle is driven aggressively, note researchers at Carnegie Mellon University's Vehicle Electrification Group.

The report's comparisons are based on simulations using the Argonne National Laboratory's Powertrain Systems Analysis Toolkit. The team's analysis appears in the online journal Energy Policy.

The analysis by Orkun Karabasoglu and Jeremy Michalek says conventional piston-powered vehicles have the lowest life-cycle costs, followed closely by hybrids. Plug-ins, which carry larger batteries and can travel farther in electric mode, come next. Pure electrics have the highest life-cycle cost.

But the researchers show that driving conditions have a huge impact on those results. A plug-in hybrid that can travel gently for 70 miles in all-electric mode can cover only 40 miles when driven aggressively.

Similarly, piston-powered cars have the lowest life-cycle costs of all powertrains analyzed. But conventional powertrains also are much more sensitive to drive cycle: Their costs are 30% higher under heavy stop-and-go driving than in mostly highway driving.

Life-cycle costs for all-electrics are the least sensitive to drive cycle. But the Carnegie Mellon team says that's only because the cost of the electricity EVs consume is small compared to the price of their batteries.

The report finds that piston, hybrid, plug-in and all-electric powertrains all produce comparable life-cycle emissions under highway driving conditions. But in city driving, hybrid powertrains care as much as 60% cleaner than piston-powered vehicles.

The Carnegie Mellon analysis questions the environmental benefit of plug-in electrics. It says emissions from plug-ins are no lower than those from conventional hybrids under most driving conditions. They also point out that a plug-in's heavier battery and the higher emissions produced in producing the battery offset the vehicle's ability to drive farther in electric-only mode.

Karabasoglu and Michalek say their analysis confirms that electric cars and plug-ins with large batteries are no more effective in reducing greenhouse gas emissions than hybrids and plug-ins with small batteries at least until the country's electric grid can get more of its electricity from sources that don't burn carbon fuels.