The Volkswagen diesel scandal convinced European regulators to switch from laboratory emissions testing to tests that involve actual, on-road driving.
This could prevent automakers from deploying "defeat device" software like the kind used by VW on laboratory tests, as well as produce results that more closely align with what consumers can expect in the real world.
But a leaked draft of new European Union emissions-testing rules indicates they could allow for significantly more air pollution, according to one advocacy group.
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Transport & Environment (T&E) claims the proposed rules would allow cars to emit up to 50 percent more than the legally-allowed level of pollutants, reports Wards Auto.
The draft regulations—called RDE3—a 50-percent "permissible tolerance" level for certain emissions in tests of gasoline direct-injection engines.
These tests would use the portable emissions measurement systems (PEMs) that are currently standard equipment for on-road emissions testing.
Portable Emissions Measurement Systems (PEMS) on a Peugeot 308
T&E acknowledges the potential for errors in on-road testing, but believes the conformity factor should be limited to 30 percent.
That figure has already been accepted by automakers, a T&E spokesperson told Wards Auto.
ALSO SEE: EU Commission Accepts 'Flawed' Emission Rules For On-Road Testing
The group is also calling for widespread use of particulate filters in the exhaust systems of gasoline cars, something it believes will result in emissions 100 times lower.
Particulate filters are common on diesel vehicles, but automakers are only just beginning to deploy them in gasoline cars.
Mercedes-Benz plans to use particulate filters on a new family of engines that will begin rolling out next year.
Mercedes-Benz 3.0-liter inline-6
Volkswagen has said it will use particulate filters on versions of the Volkswagen Tiguan crossover equipped with the 1.4-liter TSI 4-cylinder engine, and versions of the Audi A5 equipped with the 2.0-liter TFSI 4-cylinder engine.
MORE: VW will roll out particulate filters for gasoline engines next year
These models will get the filters next year, and VW may add filters to other models and engines from there.
The proposed European emissions-testing rules are currently being discussed by the EU's Technical Committee on Motor Vehicles, which is expected to vote on them before the end of the year.
After that, the European Parliament and EU Council of Ministers will have three months to accept or block the proposed rules.