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Emission Standards

EU: Heavy-Duty Truck and Bus Engines

Regulatory Framework

European emission standards for new heavy-duty diesel engines are commonly referred to as Euro I ... VI. Sometimes Arabic numerals are also used (Euro 1 ... 6). We will use Roman numerals when referencing standards for heavy-duty engines, and reserve Arabic numerals for light-duty vehicle standards.

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The emission standards apply to all motor vehicles with a “technically permissible maximum laden mass” over 3,500 kg, equipped with compression ignition engines or positive ignition natural gas (NG) or LPG engines.

The standards were originally introduced with Directive 88/77/EEC [2871], followed by a number of amendments. In 2005, the standards were re-cast and consolidated by Directive 05/55/EC [1569]. Beginning with the Euro VI stage, the legislation became simplified, as “directives”—which need to be transposed into all of the national legislations—were replaced by “regulations” which are directly applicable. The following are some of the most important rulemaking steps in the heavy-duty engine regulations:

  • Euro I standards were introduced in 1992, followed by the introduction of Euro II standards in 1996. These standards applied to both truck engines and urban buses, the urban bus standards, however, were voluntary.
  • In 1999, the EU adopted Directive 1999/96/EC [2870], which introduced Euro III standards (2000), as well as Euro IV/V standards (2005/2008). This rule also set voluntary, stricter emission limits for extra low emission vehicles, known as “enhanced environmentally friendly vehicles” or EEVs.
  • In 2001, the European Commission adopted Directive 2001/27/EC [3491] which prohibits the use of emission “defeat devices” and “irrational” emission control strategies, which reduce the efficiency of emission control systems when vehicles operate under normal driving conditions to levels below those determined during the emission testing procedure.
  • Directive 2005/55/EC [1569] adopted in 2005 introduced durability and on-board diagnostic (OBD) requirements, as well as re-stated the emission limits for Euro IV and Euro V which were originally published in 1999/96/EC. In a “split-level” approach, the technical requirements pertaining to durability and OBD—including provisions for emission systems that use consumable reagents—have been described in the Commission Directive 2005/78/EC [3492].
  • Euro VI emission standards were introduced by Regulation 595/2009 [3493], with technical details specified in a number of ‘comitology’ packages [3494][3496][3495]. The new emission limits, comparable in stringency to the US 2010 standards, became effective from 2013/2014. The Euro VI standards also introduced particle number (PN) emission limits, stricter OBD requirements and a number of new testing requirements—including off-cycle and in-use PEMS testing.

Emission Standards

The following tables contain a summary of the emission standards and their implementation dates. Dates in the tables refer to new type approvals—the dates for all vehicles are in most cases one year later.

There are two sets of emission standards, with different type of testing requirements:

  • Steady-State Testing: Table 1 lists emission standards applicable to diesel (compression ignition, CI) engines only, with steady-state emission testing requirements.
  • Transient Testing: Table 2 list standards applicable to both diesel and gas (positive ignition, PI) engines, with transient testing requirements.
Table 1
EU emission standards for heavy-duty diesel engines: Steady-state testing
Euro I 1992, ≤ 85 kW ECE R-49
1992, > 85 kW
Euro II 1996.10
Euro III 1999.10 EEV only ESC & ELR 0.15
2000.10 2.10.665.00.10a0.8
Euro IV 2005.10 1.50.463.50.020.5
Euro V 2008.10 1.50.462.00.020.5
Euro VI 2013.01WHSC×1011
a PM = 0.13 g/kWh for engines < 0.75 dm3 swept volume per cylinder and a rated power speed > 3000 min-1
Table 2
EU emission standards for heavy-duty diesel and gas engines: Transient testing
Euro III 1999.10 EEV onlyETC 3.00.400.652.00.02
2000.10 5.450.781.65.00.16c
Euro IV 2005.10 4.00.551.13.50.03
Euro V 2008.10 4.00.551.12.00.03
Euro VI 2013.01WHTC 4.00.16d0.50.460.016.0×1011
a for gas engines only (Euro III-V: NG only; Euro VI: NG + LPG)
b not applicable for gas fueled engines at the Euro III-IV stages
c PM = 0.21 g/kWh for engines < 0.75 dm3 swept volume per cylinder and a rated power speed > 3000 min-1
d THC for diesel engines
e for diesel engines; PN limit for positive ignition engines TBD

Additional provisions of the Euro VI regulation include:

  • Emission limits and requirements for off-cycle emission and in-service conformity testing, discussed later.
  • An ammonia (NH3) concentration limit of 10 ppm applies to diesel (WHSC + WHTC) and gas (WHTC) engines.
  • A maximum limit for the NO2 component of NOx emissions may be defined at a later stage.

Emission Durability. Effective 2005.10/2006.10, manufacturers should demonstrate that engines comply with the emission limit values for useful life periods which depend on the vehicle category, as shown in the following table.

Table 3
Emission durability periods
Vehicle Category†Period*
Euro IV-VEuro VI
N1 and M2100 000 km / 5 years160 000 km / 5 years
N3 ≤ 16 ton
M3 Class I, Class II, Class A, and Class B ≤ 7.5 ton
200 000 km / 6 years300 000 km / 6 years
N3 > 16 ton
M3 Class III, and Class B > 7.5 ton
500 000 km / 7 years700 000 km / 7 years
† Mass designations (in metric tons) are “maximum technically permissible mass”
* km or year period, whichever is the sooner

Effective 2005.10/2006.10, type approvals also require confirmation of the correct operation of the emission control devices during the normal life of the vehicle under normal conditions of use (“conformity of in-service vehicles properly maintained and used”).

Early Introduction of Clean Engines. EU Member States are allowed to use tax incentives in order to speed up the marketing of vehicles meeting new standards ahead of the regulatory deadlines. Such incentives have to comply with the following conditions:

  • they apply to all new vehicles offered for sale on the market of a Member State which comply in advance with the mandatory limit values set out by the Directive,
  • they cease when the new limit values come into effect
  • for each type of vehicle they do not exceed the additional cost of the technical solutions introduced to ensure compliance with the limit values.

Euro VI type approvals, if requested, must have been granted from 7 August 2009, and incentives could be given from the same date. Euro VI incentives can also be given for scrapping existing vehicles or retrofitting them with emission controls in order to meet Euro VI limits.

Early introduction of cleaner engines can be also stimulated by such financial instruments as preferential road toll rates. In Germany, road toll discounts were introduced in 2005 which stimulated early launch of Euro V trucks.


The regulatory emission test cycles have been changed several times, as indicated in Table 1 and Table 2. At the Euro III stage (2000), the earlier steady-state engine test ECE R-49 was replaced by two cycles: the European Stationary Cycle (ESC) and the European Transient Cycle (ETC). Smoke opacity was measured over the European Load Response (ELR) test. Since the Euro VI stage, engines are tested over the WHSC and WHTC tests. In addition, the Euro VI regulation introduced off-cycle and in-service conformity testing. The following are some of the important testing requirements:

  • Euro III: ESC/ELR test for conventional diesel engines; ESC/ELR + ETC testing for diesel engines with “advanced aftertreatment” (NOx aftertreatment or DPFs) and for EEVs; ETC test for positive ignition (NG, LPG) engines.
  • Euro IV-V: ESC/ELR + ETC test for diesel engines; ETC test for positive ignition engines.
  • Euro VI testing:
    • Type approval testing:
      • WHSC + WHTC test for diesel engines; WHTC test for positive ignition engines,
      • Off-cycle emission (OCE) testing:
        • NTE engine testing over the WNTE cycle, and
        • PEMS vehicle test.
    • In-service conformity (ISC): In-use vehicle PEMS testing.

Some Euro VI provisions, including OCE/ISC testing and OBD requirements, are phased-in over several years. The corresponding stages of the emission standards are referred to as Euro VI-A through Euro VI-E, Table 4.

Table 4
Euro VI stages and OCE/ISC requirements
StageImplementation DateOCE/ISC Requirements
Type approval (new types/all vehicles)Last date of registrationPEMS power thresholdCold start included in PEMSOCE
A2013.01/2014.012015.0920%NoNOx 0.60
THC 0.22
CO 2.0
PM 0.016
B (CI)2013.01/2014.012017.01
B (SI)2015.09/2015.092017.01

Off-Cycle Testing. Euro VI regulation introduced off-cycle emissions (OCE) testing requirements. OCE measurements, performed during the type approval testing, have two elements: laboratory testing following the NTE (not-to-exceed) limit approach and in-use PEMS testing.

In the NTE limit approach, a control area is defined on the engine map (there are two definitions, one for engines with a rated speed < 3000 rpm, and another for engines with a rated speed ≥ 3000 rpm). The control area is divided into a grid. The testing involves the random selection of three grid cells and emission measurement at 5 points per cell. The Euro VI emission limits for NTE testing are shown in Table 4.

The PEMS procedure at type approval is similar to the ISC PEMS testing discussed below. Differences include: type-approval PEMS testing can be done on a prototype or modified production vehicle and testing is carried out at a payload between 50-60%.

In-Service Conformity Testing. The Euro VI regulation also introduced in-use testing requirements that involve field measurements using PEMS. The testing is conducted over a mix of urban (0-50 km/h), rural (50-75 km/h) and motorway (> 75 km/h) conditions, with exact percentages of these conditions depending on vehicle category. ISC testing is required within 18 months of the first registration, on a vehicle registered in the EU that has accumulated a minimum of 25,000 km.

During the test, emissions are averaged using the “averaging window” method. It is a moving average process, where the duration of the averaging period (window) is determined based on the mechanical work or CO2 emission that were measured over the WHTC test during type approval testing. Up to and including Euro VI-D, cold start emissions are excluded. For Euro VI-C and earlier, windows with an average power of 20% or less of the maximum engine power are excluded. For Euro VI-D and later, this power threshold is 10%. Type approval authorities can request that the vehicle be tested with any payload between 10-100%.

A conformity factor (CF) of 1.5 applies to gaseous emissions. To pass the test, the 90th percentile of the measured emissions must not exceed the CF × WHTC emission standard for the respective components. Starting with Euro VI-E, ISC testing will include cold start as well as PN emissions.