Comparison to other modes of transportation

Figure 3.11: The variation in the specific fuel consumption per RPK when using four different methodologies for attributing fuel to freight

RPK1 represents the methodology where all the fuel is attributed to passenger transport.

RPK2 represents the methodology where the fuel is distributed equally between passengers and freight on a weight basis. RPK3 represents the methodology where the weight of the passengers is multiplied by a factor of 1,7 before distributing the fuel consumption between the weight of passengers and freight. RPK4 represents the methodology where the weight of the passengers is multiplied by 2.5. The examples here are for selected aircraft operated by American air carriers in 1999. The average passenger loads factors as well as the average freight weight may vary considerable between airlines and may change from year to year.

Sources: Fuel consumption from [DOT 2001] and freight loads from [Air Transport Association 1999, 2000e and 2001].

examples of intra-European and intra-American routes where air transport is relatively cheap as compared to rail and bus. This section does not consider these economical and infrastructure aspects but merely compares the fuel intensity of air transport to other modes. The focus chosen is to study short-distance and medium-distance (up to a few thousand kilometres) passenger travel in aircraft, passenger cars, buses and trains.

First of all, it has to be mentioned that comparisons of the environmental impact of different transport modes are problematic, as each mode of transport generates different kinds of environmental problems. Additionally, the environmental impact is often site specific. For instance car exhaust creates other problems in cities than it does in rural areas, and it is difficult to compare health problems in cities created by exhaust from cars, buses and trucks to high altitude aircraft emissions contributing to climate change. Furthermore, a wide variety of vehicles with different characteristics makes it difficult to establish average pollution indexes for each mode of transportation.

This has been exemplified in the earlier sections of this chapter that show the marked differences in the fuel intensity of old and new aircraft as well as differences between small short haul aircraft and larger medium-haul and long haul aircraft types. Another problem in such comparisons is the variability in the fuel consumption and emissions related to differences in the usage cycles for vehicles. For example, the fuel efficiency of aircraft depends strongly on the actual stage distance. For trains, one important factor to take into account is the number of stopovers at a given trip, while for passenger cars the fuel efficiency varies strongly between city and highway driving.

Another factor is the level of traffic on roads and rails and in airports where congestion is often a problem for the flow of traffic. Furthermore, the actual load factor of passenger cars, buses, trucks, trains and aircraft plays an important role. A special feature of aircraft is furthermore that they most often fly more direct routings than for example road traffic. When comparing the fuel intensity per passenger kilometre this factor also has to be taken into account. Therefore, the average estimates given here should merely be taken as examples.

Most of the major scheduled airlines emit between 125-175g of CO2 per revenue passenger kilometre (RPK). The most efficient European charter airlines emit around 109g of CO₂ per RPK on medium-haul routes while the least efficient short-haul regional scheduled carriers emit more than 250g of CO₂ per RPK. That is, the 109g of

CO2 per RPK represents the minimum emissions from holiday travel over distances of at least 2000 kilometres whereas the 250g represents the maximum emissions from scheduled flights over short distances.

Figure 3.12 illustrates the mileage of different car models available for sale in Denmark in 1998 according to their energy labelling that is based on test data for an average European standard driving cycle. In 1999 and 2000, some more fuel-efficient models have been introduced, most notably the VW LUPO 3L TDI rated at 33 kilometres per litre of diesel. We note that such test data may overestimate the mileage because the actual driving cycle may be more fuel intensive [Schipper and Marie-Lilliu 1999]. The fuel efficiency of passenger cars is very much dependent upon the weight of the car.

Light cars generally drive longer per litre of fuel than heavier cars [Færdselsstyrelsen 1999].

Figure 3.12: Fuel efficiency rating of passenger cars for sale in Denmark 1998

Source: [Færdselsstyrelsen 1999]

The average on the road CO2 intensity of passenger cars differs widely between countries. For example the average United States passenger car emits around 272g CO₂ per vehicle kilometre whereas for example the average Dutch car emits around 193g⁴⁹. These differences are largely due to differences in the fleet mix as well as driving cycles [Schipper and Marie-Lilliu 1999]. The CO₂ intensity per passenger

5 10 15 20 25

0,5 0,7 0,9 1,1 1,3 1,5 1,7 1,9 2,1 2,3 2,5

Weight of the car (tonnes)

kilometres per litre of fuel Diesel (km/liter)

Petrol (km/liter)

kilometre of a given trip furthermore depends on the load factor. The average passenger load factors are found to vary from country to country [Schipper and Marie-Lilliu 1999] [IPCC 1996b, 693] [EEA 2000 and 2001] and tends to be higher in for example European holiday traffic than in average everyday traffic [Roos et. al. 1997].

According to Roos et. al. [1997, p.26] the total fuel consumption per vehicle kilometre of a small car with four occupants may be around 14% higher than for a similar car with one occupant (larger cars are less sensitive in this respect). When used for long-distance travel most passenger cars may drive longer on each litre of fuel than in an average European driving cycle. Furthermore, if the car carries a caravan, the fuel consumption per kilometre may increase by 50-100% [Roos et. al. 1997]. Additionally, a comparison to aircraft should take into account that cars drive longer distances between destinations than aircraft and that passenger cars may have to cross waters by ferry to reach the destination. A study of the specific fuel consumption of passenger cars and other modes on distances between eight European city-pairs takes these factors into account. The study concludes that an average car with two occupants is typically as fuel-efficient as modern turboprops (Fokker 50s) and jets (B737-400s) that operate at these specific distances. This study thereby indicates that at passenger load factors of three or more persons the passenger car is typically more fuel-efficient than aircraft [Roos et. al 1997].

A number of studies from around the World have found that trains and coaches are generally less fuel-intensive than passenger cars and aircraft [IPCC 1996b] [Roos et.

al. 1997] [IPCC 1999, p. 285]. For example, a long haul coach with a 70% occupancy rate typically emits around 20-30g of CO₂ per passenger kilometre or around 80% less than an average two-occupant passenger car [Roos et. al. 1997, p. 82] [Jørgensen 1998]. The emission of CO₂ per passenger kilometre of electrical trains depends on the primary fuel used for the power production and on the overall efficiency of the production and transmission system. High speed electrical trains, such as the German ICE and the French TGV emit 41g and 7g of CO2 per passenger kilometre respectively⁵⁰. However, if the TGV train had used electricity produced by the electrical system in for example Denmark (in 1996) where the fuel mix is based mainly on coal

49 These estimates are for 1995.

50 Based on an average consumption of 78,9Mje/km, 51% load factor and 159g CO2 emissions per MJ electricity produced for the German ICE train. Based on an average consumption of 68,5Mje/km, 65% load factor and 31,3g CO2 emissions per MJ electricity produced for the French TGV train [Roos et. al. 1997, p. 101].

and other fossil fuels, the CO2 emissions from the TGV train would be around 7 times higher [Roos et. al 1997, p. 101]. Likewise, the Danish inter-city electrical and diesel trains emit around 13-21g of CO2 per available seat kilometre or around 26-42g at a load factor that is comparable to that of the German ICE train [DSB 2001].