TravelFootprint

The Travelfootprint tool assesses the impacts of the main modes of passenger travel in the UK. As many comparative studies have done before, the analysis includes an assessment of the environmental impacts associated with the fuel cycle (primary production, extraction, transportation, refining, and vehicle operation) for each of the modes includes in the tool. Unlike previous UK studies, the analysis also assesses the impacts associated with the vehicle cycle (vehicle manufacture, assembly and disposal).

Although the environmental impacts of fuel and vehicle cycles include a wide range of resource, pollutant and land-use issues, the analysis focuses exclusively on quantifying the extent and impacts of life cycle air-borne emissions arising from the fuel and vehicle cycles. The air emissions assessed include the regulated emissions: carbon monoxide, oxides of nitrogen, hydrocarbons and particulates. In addition, the three main greenhouse gases (climate change) associated with transport are assessed: carbon dioxide, nitrous oxide and methane. The greenhouse gas emissions are combined to provide a single measure of greenhouse gas emissions by using accepted global warming potentials for each of the gases assessed.

In addition to making lifecycle emissions comparisons for each of the travel modes considered, the analysis makes an impact assessment as part of the life cycle emission methodology. This is achieved by the use of the Environmental Rating Tool developed by the European Cleaner Drive Programme. This rating system uses recognised external costs to establish the relative weight to attach to different emissions the external costs are values expressed in monetary terms that reflect the overall damage to the environment and to human health caused by emissions.

Using the Cleaner Drive rating system, the level of environmental impact is expressed as a score between 0-100, which indicates the overall impact of both regulated pollutants (air quality) and greenhouse gases (climate change). For clarity, the original Cleaner Drive scoring system has been reversed for the Travelfootprint tool so that travel modes with lower emissions have a lower environmental rating (a lower score). The most sustainable method of travel would therefore score 0 (zero). For travel modes with very high life cycle emissions, the rating score can very occasionally be greater than 100 (this occurs where vehicle CO2 emissions are greater than 300 grams/km).

The Travelfootprint tool uses the methodology developed for a previous Camden LCA study (see About) and extends the application beyond passenger cars to include the main passenger travel modes. Where necessary, the methodology input data has been modified to account for travel modes not considered by the original study (eg emissions from aircraft). For more information on the original methodology used, see the original report entitled Life Cycle Assessment of Vehicle Fuels and Technologies, which can be downloaded in pdf format here: LCA Report 2006 (1MB)

In preparing the data for the new Travelfootprint website, the modal CO2 emission data has been compared with the Passenger Transport Emission Factors Report (Methodology Paper) published by DEFRA in 2007 Where a direct comparison is possible, most modes show a high degree of agreement – with the exception of air travel; the difference can be explained by the use of a 2.7 radiative forcing (CO2) factor to represent the increased impact of emissions at altitude, which is not used by the DEFRA analysis.

Analysis of travel modes

As far as possible, all travel modes (walking, cycling, bus, rail, etc) are analysed on the same basis. In summary, each travel mode is analysed as follows (a report giving more details of the analysis for each travel mode will be published in August 2008):

WALK & CYCLE - emissions assessed include: those produced during respiration (breathing), food production, and generated in obtaining the energy required to maintain basic metabolism (body function and repair), and in the case of cycling, produced as a result of bicycle manufacture. Food produced using non-organic and organic methods is assessed, as is food that is imported or produced close to the point of consumption. The main approach is to assess the percentage of EU emissions that are associated with food and beverage consumption, and combine this with published annual (average) mileages and metabolic rates for walking and cycling in the UK. Refs: EIPRO Environmental Impact of Products, Analysis of the life cycle environmental impacts related to the total final consumption of the EU25, 2005; Coley, D.A., 2001, Emission Factors for Human Activity. Energy Policy, 30(1):3-5; DEFRA Emission Statistics 1006.

MOTORCYCLE - emissions assessed include: those produced during vehicle use, as well as emissions generated during fuel production and distribution, and vehicle manufacture and assembly. Two-stroke, four-stroke and electric motorcycles are assessed for a range of passenger loadings. The main approach is to sum tailpipe emissions with those produced during fuel production and vehicle manufacture. Refs: L. Ntziachristosa et al. (2006), Emission control options for power two wheelers in Europe, Atmospheric Environment 40 (2006) 4547–4561; World Motorcycle Test Cycle data.

CAR & TAXI - emissions assessed include: those produced during vehicle use, as well as emissions generated during fuel production and distribution, and vehicle manufacture and assembly. The main approach is to sum tailpipe emissions with those produced during fuel production and vehicle manufacture. Petrol, diesel, liquefied petroleum gas, compressed natural gas, bioethanol E85, petrol hybrid, and battery electric cars are assessed for a range of passenger loadings. Using the Cleaner Drive methodology, overall environmental impacts are calculated for specific car models (since 2001) and also for the average in each vehicle class (eg small family car). Main refs: see below.

BUS - emissions assessed include: those produced during vehicle use, as well as emissions generated during fuel production and distribution, and bus manufacture and assembly. The main approach is to sum tailpipe emissions with those produced during fuel production and vehicle manufacture. Diesel buses over four different Euro emission standards (which approximately correspond to vehicle age) are assessed for a range of passenger loadings. Refs: National Atmospheric Emissions Inventory database v02.8.xls, NETCEN 2003; Bus and Light Rail Statistics GB: Department for Transport, Statistics Bulletin (06)18, January - March 2006

RAIL & LONDON UNDERGROUND - emissions assessed include: those produced during train use, as well as emissions generated during fuel production and distribution. Emissions generated during train manufacture and assembly are not included in the analysis, as these are considered insignificant over the life of the vehicle. For national rails services, diesel-electric, diesel and electric locomotives and multiple-unit trains are assessed for a range of passenger loadings. For London Underground, emission factors are based on the London Underground's annual electricity consumption and uses corresponding passenger km figures for the Underground from TfL. Refs: Rail Emission Model (prepared for the Strategic Rail Authority), AEA Technology, 2001; Melanie Hobson (one of the authors of previous report), private communications; Passenger Transport Emission Factors, Methodology Paper, DEFRA, 2007; Environmental Report, Transport for London, 2006.

FLY - emissions assessed include: those produced during vehicle use, as well as emissions generated during fuel production and distribution. The main approach is to combine the emissions associated with Landing and Taxi-off Cycle (LTO) which includes emissions up to 1000m altitude, with cruise phase emissions. Emissions generated during aircraft manufacture and assembly are not included in the analysis, as these are considered insignificant over the total life of the aircraft. Passenger-jets analysed include the Boeing 737-400 and 747-400, the emissions of which are used to estimate typical generic domestic (UK), short- and long-haul (international) aircraft emissions impacts. The analysis includes the use of a 2.7 radiative forcing (CO2) factor to represent the increased impact of emissions at altitude. Refs: EMEP/CORINAIR Emissions Inventory Guidebook, Chapter B851 on aviation, 2001; The Environmental Effects of Civil Aircraft in Flight, Royal Commission on Environmental Pollution (RCEP), 2002.

Main research references

To demonstrate the level of research underlying the science and analysis used by the Travelfootprint tool, here is a selection of the main references used to inform the vehicle calculations. A more comprehensive reference list is contained within the original report entitled Life Cycle Assessment of Vehicle Fuels and Technologies, which is available for download (see above).

Concawe (2005/06) Well-To-Wheels Analysis Of Future Automotive Fuels And Powertrains In The European Context. Report by Concawe, Eurcar and the EU Joint Research Centre, 2005/06.

Daniels E.J., J.A. Carpenter and P.S. Sklad (2004) Automotive Lightweighting Materials. FY 2004 Progress Report. Argonne National Laboratory. Also personal communication.

ETSU (1996) Alternative Road Transport Fuels: A Preliminary Life-cycle Study for the UK, Volume 2, ETSU. London, The Stationary Office.

Funazaki A., K. Taneda, K. Tahara and A. Inaba. (2003) Automobile life cycle assessment issues at end-of-life and recycling. JSAE Review, Volume 24, Issue 4, October 2003, pp381-386.

IAI (2003) Life Cycle Assessment of Aluminum: Inventory Data for the Worldwide Primary Aluminum Industry. International Aluminum Institute, 2003.

IISI (2002) World Steel Life Cycle Inventory. Methodology Report. International Iron and Steel Institute. Committee on Environmental Affaires, Brussels, 2002.

IPAI (2000) Life Cycle Inventory of the Worldwide Aluminum Industry with Regard to Energy Consumption and Emission of Greenhouse Gases. Paper 1 Automotive. International Primary Aluminum Institute, 2000.

MacLean, H. and L. Lave (2002) Evaluating automobile fuel/propulsion systems technologies. Progress in Energy and Combustion Science 29; pp.1-69.

Mierlo J.V., J-M. Timmermans, G. Maggetto, P. V. den Bossche, S. Meyer, W. Hecq, L. Govaerts and J. Verlaak (2004) Environmental rating of vehicles with different alternative fuels and drive trains: a comparison of two approaches. Transportation Research Part D 9 (2004) 387399

Rydh J. and M. Sun (2005) Life cycle inventory data for materials grouped according to environmental and materials properties. Journal of Cleaner Production (13) pp.1258-1268.

Schweimer G.W. and M. Levin (2000) Life Cycle Inventory for the Golf A4. Research, Environment and Transport, Volkswagen AG, Wolfsburg, Germany.

Sullivan (1998) Life Cycle Inventory of a Generic US Family Sedan. Overview of Results USCAR AMP Project. Ford Motor Co.

Zamel N. and X. Li (2005) Life cycle analysis of vehicles powered by a fuel cell and by internal combustion engine for Canada. Journal of Power Sources. In press.