The current emission-measuring technique for type-testing passenger vehicles stems from the 1970s and was modified in the 1990s. It is extremely out of date and fails to factor in electronic control systems—the enablers of the emissions cheating behind current diesel scandals. Between 2009 and 2011 various workgroups were formed under the umbrella of the UN’s Economic Commission for Europe to develop a new emission-measuring method called the Worldwide Light Duty Vehicle Test Procedure (WLTP). The team included experts from the Swiss Federal Office for the Environment (FOEN), the Federal Roads Office (FEDRO), Bern University of Applied Sciences and Empa.

The new regulations for passenger vehicles contain three main changes:

1. The outdated measuring technique will be replaced;

2. Exhaust emissions will have to be determined in addition while driving on the roads; and

3. The manufacturers will have to disclose the engine control unit functions connected with exhaust gas purification.

Empa says that the most challenging aspect of the new emissions legislation will be the road measurements, which involve an at least 90-minute journey with predefined proportions on city, country and highway roads. To this end, a mobile emission measuring device will be installed on the vehicle.

An Audi A3 with the measuring backpack to gage RDEs (real driving emissions). As of 1 September 2017, these emission measurements in actual road traffic will be mandatory for the approval of new vehicle types. Image: Empa. Click to enlarge.

As usual, the introduction of new emissions regulations for passenger vehicles and light utility vehicles will be staggered. Vehicles that already have a type approval may normally be approved for another year beyond the date the new emissions level is introduced.

Specifically, this means that passenger vehicles that have been type-approved in accordance with the existing emissions norm Euro 6b can still be approved until the end of August 2018. As diesel vehicles that have been type-approved in accordance with this stage usually display much higher NO_x emissions on the road than in the lab, Empa recommends no longer purchasing such vehicles.

The new emissions regulations will be introduced in three stages. The first stage, Euro 6c, does not yet contain any limits for road measurements. Due to the new regulations on disclosing exhaust gas purification functions in the engine control unit, the NO_x emissions may still drop significantly compared to existing Euro 6b vehicles. The Euro 6c passenger vehicles may be approved until the end of August 2019 and constitute a stepping stone towards clean diesel.

However, gasoline vehicles are also affected by the new regulations: For gasoline cars with direct injection engines, the same particle number limit applies from level Euro 6c as for diesel vehicles, which is why most gasoline cars will not really be able to dispense with particle filters in future. Only natural gas vehicles meet the new emissions regulations without any additional technical measures.

The emissions standard Euro 6d will ultimately be introduced in two stages: The first, referred to as Euro 6d-TEMP, will apply from September 2019 to the end of 2020 and, for the first time, contains both NO_x and particle number limits for road measurements—which may still be up to 2.1 times higher than the corresponding lab limits, however.

In the second stage, emission standard Euro 6d, the factor for the deviation between road and lab limits will fall to 1.5. For reasons of air hygiene, Empa recommends only buying diesel vehicles in accordance with Euro 6d-TEMP or Euro 6d.

The new emissions legislation also closes various loopholes: Until now, vehicles that are sometimes considerably lighter in the lab test than when they drive around streets in the real world could be tested. Under the new regulations, the lightest and heaviest versions of the vehicle need to be tested.

Also up to now, vehicle manufacturers have not had to provide any details on their emissions control. With the new disclosure provisions on the exhaust gas purification functions in the engine control unit, this is no longer possible. The most important improvement, however, is the introduction of realistic road measurements, which will ensure that the discrepancy between lab readings and real-world emissions is reduced significantly.

Empa’s bottom-line buying recommendation: at least Euro 6c for gasoline cars, at least Euro 6d-TEMP for diesel.