1.A.3.c - Transport: Railways

In category 1.A.3.c - Railways, emissions from fuel combustion in German railways and from the related abrasion and wear of contact line, braking systems and tyres on rails are reported.

Germany's railway sector is undergoing a long-term modernisation process aimed at making electricity the main energy source for rail transports. Use of electricity, instead of diesel fuel, to power locomotives has been continually increased, and electricity now provides over 80% of all railway traction power. Railways' power stations for generation of traction current are allocated to the stationary component of the energy sector (1.A.1.a) and are not included in the following. In energy input for trains of German railways, diesel fuel is the only energy source that plays a significant role apart from electric power.

Generally, total inland deliveries of diesel oil are available from the National Energy Balances (NEBs) (AGEB, 2025) ¹⁾. This data is based upon sales data of the Association of the German Petroleum Industry (MWV) ²⁾. As a revision of this MWV data for the years 2005 to 2009 was not adopted to the respective National Energy Balances, the original MWV data are applied for this five years.

Data on the consumption of biodiesel in railways is provided in the NEBs as well, from 2004 onward. However, the data applied in the emissions inventory are based on the average annual shares of biodiesel added to the fossil diesel oil.

In addition, rather small quantities of solid fuels are used for historical steam engines vehicles operated mostly for tourism and exhibition purposes. Official fuel delivery data are available for lignite, through 2002, and for hard coal, through 2000 only. Therefore, in order to complete these time series, operator surveys were carried out in 2012 ³⁾, 2016 ⁴⁾ and 2021 ⁵⁾. During these surveys, questionnaires were provided to any known operator of historical steam engines in Germany. Here, due to limited data archiving, nearly complete data could only be gained for years as of 2005 and for the main operators only. For earlier years and a variety of smaller operators, conservative gap filling was applied.

Table 1: Overview of activity-data sources for domestic fuel sales to railway operators

Table 2: Annual fuel consumption in German railways, in terajoules

The use of other fuels – such as vegetable oils or gas – in private narrow-gauge railway vehicles has not been included to date and may still be considered negligible.

For estimating abrasive emissions of PM and heavy metals from wheel on track, brakes and contact line (electric traction only), annual transport performance data is applied, representing the trains gross weight (locomotive + waggons + freight) times the mileage driven and provide by the Deutsche Bahn in performance ton-kilometers [Ptkm].

Table 3: Annual transport performance by mode of traction, in Mio Ptkm (performance ton-kilometers)

Transport performance showed only a moderate pandemic-related decrease in 2020 and has fully recovered in 2021 and 2022.

Regarding particulate-matter and heavy-metal emissions from abrasion and wear of contact line, braking systems, tyres on rails, annual transport performances of railway vehicles with electrical and Diesel traction derived from Knörr et al. (2025a) ⁶⁾ are applied as activity data.

The (implied) emission factors used here for estimating emissions from diesel fuel combustion are of very different quality:

For the main pollutants, CO and PM, annual tier2 IEF computed within the TREMOD model are used, representing the development of German railway fleet, fuel quality and mitigation technologies ⁷⁾. (see next table).

Table 3: Annual country-specific emission factors for diesel fuels¹, in kg/TJ

Regarding emissions from solid fuels used in historic steam engines, all emission factors displayed below have been adopted from small-scale stationary combustion.

Table 4: Emission factors applied for solid fuels, in kg/TJ

Table 5: Tier1 emission factors applied to railway vehicles, in [g/TJ]

Here, as the EMEP/EEA Guidebook 2023 does not provide specific defaults for Pb, Hg and As, the EF applied here has been derived from chapter: 1.A.3.b i-iv, tier1 value for heavy-duty diesel vehicles.

Regarding the POPs to be reported, tier1 emission factors have been derived from different sources. For B[a]P, B[b]F, B[k]F, and I[123cd]P from diesel railway engines, tier1 values as provided in the EMEP/EEA Guidebook 2023 in chapters 1.A.3.c and 1.A.3.b (Update 2024) are used. Here, as no tier1 defaults specific to railways are provided for B[k]F and I[1,2,3-cd]P, the values provided for road heavy-duty vehicles are applied instead, as proposed in Table 3-9 in chapter 1.A.3.c of the EMEP/EEA Guidebook 2023 ¹¹⁾.

For dioxins and furans (PCDD/F), as the EMEP/EEA Guidebook 2023 ¹²⁾, chapter 1.A.3.c Railways, Table 3-1: Tier 1 emission factors for diesel railways does not provide a tier1 value, the EF has been derived from a study carried out by Rentz et al. (2008) ¹³⁾ for the German Federal Environment Agency. Furthermore, both HCB and PCBs emissions are stated as not applicable in the EMEP/EEA Guidebook 2023 ¹⁴⁾, . Therefore, these emissions are only calculated for firewood (HCB) and fossil solid fuels (PCBs), respectively, with EF adopted from stationary combustion.

Table 6: Tier1 emission factors applied to railway vehicles

Regarding emissions from abrasion and wear, emission factors are calculated from PM₁₀ emission estimates directly provided by the German railroad company Deutsche Bahn AG.

As these original emissions are only available as of 2013, implied EF(PM₁₀) ara calculated from the emission estimates extrapolated backwards from 2013 to 1990 based on the transport performance data available from TREMOD.

Here, within the underlying DB model, emission factors for PM₁₀ emissions from tyre on rail and gray cast iron brakes were revised already with the previous submission to take into account recent information gained during a measurement campaign (“Size-specific and spatial distribution of traffic-related abrasion and particulate emissions” (Größenspezifische und räumliche Verteilung von verkehrsbedingten Abrieben und partikulären Emissionen) carried out by TU Graz for the German Centre for Rail Traffic Research (DZSF - Deutsches Zentrum für Schienenverkehrsforschung). ¹⁷⁾

Regarding PM_2.5, and TSP, due to leck of better information, a fractional distribution of 0.5 : 1 : 1 (PM_2.5 : PM₁₀ : TSP) is assumed for now. Emission factors for emssions of copper, nickel and chrome are calculated via typical shares of the named metals in the contact line (copper) and in the braking systems (Ni and Cr). Other heavy metals contained in alloys used for the contact line (silver, magnesium, tin) are not taken into account here. Furthermore, emissions from other wear parts (e.g. the current collector) are not estimated. However, these components are not supposed to contain any of the nine heavy metals to be reported here (current collectors are made of aluminium alloys and coal).

Table 7: Country-specific emission factors for abrasive emissions, in [mg/performance-tonnes km]

Table 6: Outcome of Key Category Analysis

Basically, for all unregulated pollutants, emission trends directly follow the trend in over-all fuel consumption.

Here, as emission factors for solid fuels tend to be much higher than those for diesel oil, emission trends are disproportionately effected by the amount of solid fuels used. Therefore, for the main pollutants, carbon monoxide, particulate matter and PAHs, emission trends show remarkable jumps especially after 1995 that result from the significantly higher amounts of solid fuels used.

For all fractions of particulate matter, the majority of emissions generally result from abrasion and wear and the combustion of diesel fuels. Additional jumps in the over-all trend result from the use of lignite briquettes (1996-2001). Here, as the EF(BC) for fuel combustion are estimated via fractions provided in ¹⁸⁾, black carbon emissions follow the corresponding emissions of PM_2.5.

Due to fuel-sulphur legislation, the trend of sulphur dioxide emissions follows not only the trend in fuel consumption but also reflects the impact of regulated fuel-qualities. For the years as of 2005, sulphur emissions from diesel combustion have decreased so strongly, that the over-all trend shows a slight increase again due to the now dominating contribution of sulphur from the use of solid fuels.

Regarding heavy metals, emissions from combustion of diesel oil and from abrasion and wear are estimated from tier1 default emission factors. Therefore, the emission trends reflect the development of diesel use and - for copper, chromium and nickel emissions resulting from the abrasion & wear of contact line and braking systems - the annual transport performance (see description of activity data above).

Activity data have been recalculated due to the finalization of the National Energy Balances 2023 ¹⁹⁾. In addition, the shares of blende biodiesel have been revised for all years as of 2004.

Table 5: Revised energy inputn data, in terajoules [TJ]

Furthermore, due to the routine revision of the TREMOD model ²⁰⁾, tier2 emission factors changed slightly for recent years.

In contrast, transport performance data as well as the corresponding emission factors applied for the estimation of abrasive particulate matter and heavy metals (Cu, Ni, Cr) emissions remain unaltered.

Uncertainty estimates for activity data of mobile sources derive from research project FKZ 360 16 023 (title: “Ermittlung der Unsicherheiten der mit den Modellen TREMOD und TREMOD-MM berechneten Luftschadstoffemissionen des landgebundenen Verkehrs in Deutschland”) carried out by Knörr et al. (2009) ²¹⁾.

Besides the scheduled routine revision of TREMOD, no further improvements are planned for the next annual submission.

Why are similar EF applied for estimating exhaust heavy metal emissions from both fossil and biofuels?

The EF provided in the 2023 EMEP/EEA Guidebook ²²⁾ represent summatory values for (i) the fuel's and (ii) the lubricant's heavy-metal content as well as (iii) engine wear. Here, there might be no heavy metals contained in the biofuels. But since the specific shares of (i), (ii) and (iii) cannot be separated, and since the contributions of lubricant and engine wear might be dominant, the same emission factors are applied to biodiesel.