The Volkswagen diesel scandal has led to calls for more real-world emission testing outside laboratory conditions, in order to catch future cheating.

That could be bad news for hybrids and plug-in hybrids, claims a former Fiat executive.

Rinaldo Rinolfi, the former head of powertrain research at the Italian carmaker, claims that plug-in hybrids in particular will do worse on the real-world emissions tests that many are calling for.

DON'T MISS: EU Commission Accepts 'Flawed' Emission Rules For On-Road Testing

A newfound focus on real-world testing will ultimately hurt hybrids and plug-in hybrids, Rinolfi said in a recent interview with Automotive News Europe (subscription required).

In Europe at least, Rinolfi said, current laboratory testing of plug-in hybrids produces fuel-economy results that are 30 to 40 percent higher than what drivers get in the real world.

Hybrids without plugs may be affected as well, but to a lesser extent, he said.

2015 Volkswagen Passat GTE (European spec)

2015 Volkswagen Passat GTE (European spec)

The results, of course, largely depend on how much any testing cycle weights stop-and-go city driving—where hybrids tend to do better—against highway driving, he said.

Plug-in hybrids are particularly hard to rate for fuel economy, because owners will achieve vastly different results depending on how often they plug in.

Any standardized test cycle must inevitably make assumptions about the balance of engine- and battery-powered miles that may differ from actual owners' results.

ALSO SEE: U.S. Emission Tests Are Unrealistic, But European Testing Is Far Worse (Oct 2015)

By contrast, Rinolfi was comparatively optimistic about the future of diesel cars in Europe.

He predicts that diesel's dominance of the European market is ending, but that diesel's share of that market will stabilize at 40 percent by 2020, down from today's 50 percent.

But that's because of the Volkswagen diesel cheating scandal, he said.

2017 Mitsubishi Outlander PHEV

2017 Mitsubishi Outlander PHEV

Rather, it's due to stricter Euro 6 emissions standards—which will roughly match U.S. standards implemented in 2007 by next January—that make diesel vehicles more expensive to manufacture.

"I do not believe the VW scandal had any meaningful effect" on European diesel demand, he said.

That's quite a contrast to the U.S., where the already-small market for diesel passenger cars has imploded since the scandal began last September.

MORE: European electric and plug-in hybrid sales for January-February 2016

Looking to the future, Rinolfi was skeptical about battery-electric cars, saying much greater advancements in battery technology are needed for them to become truly mainstream.

There also "is not much more that can be invented" to improve conventional gasoline engines, he said.

Instead, Rinolfi advocates compressed natural gas (CNG) as a cost-effective solution to lowering the carbon emissions of road vehicles.

2012 Honda Civic Natural Gas

2012 Honda Civic Natural Gas

Used mostly in commercial vehicles in the U.S., natural gas has failed to gain widespread adoption in North America because fueling infrastructure to support it has failed to appear.

[hat tip: Brian Henderson]


Follow GreenCarReports on Facebook and Twitter