3.3.1. Energy Use per Private Passenger Vehicle Kilometer

Table 3 shows that energy use per private passenger vehicle kilometer varies from a high of 4.9 mega-joules per km (MJ/km) in Canadian cities (4.8 MJ/km in Asian cities and 4.1 MJ/km in the American and Australian cities), down to 2.3 MJ/km in Umeå and 2.4 MJ/km in Stockholm. It must be borne in mind, however, that the data for the Swedish cities and Freiburg are from 2015, ten years later than the data for US, Australian, Canadian, European and Asian cities, over which time, technological advances and changes in the size and weight of vehicles may have yielded increases in the fuel efficiency of vehicles. It might be that 2015 data for the other cities could show lower rates of energy use per vehicle kilometer than they did in 2005, though the relativities between cities are likely to remain similar. Figure 3 summarizes these results.

**Figure 3.** Energy use per vehicle kilometer in private passenger transport in ten Swedish cities (2015); Freiburg (2015); and American, Australian, Canadian, European and Asian cities (2005–2006).

The larger Swedish cities consume, on average, 3.1 MJ/km in private passenger modes, which is the same as the European cities, while the small cities consume 2.9 MJ/km (less congestion and higher vehicle operating speeds may partly explain this—see Section 4). Freiburg has the same rate of energy use as the larger Swedish cities (3.1 MJ/km). The range in energy use per VKT in private passenger transport in Swedish cities is from 2.3 MJ/km (Umeå) to 3.5 and 3.6 MJ/km in Linköping and Jönköping, respectively.

3.3.2. Energy Use per Public Transport Vehicle Kilometer

Whilst it has been explained that energy use per VKT for public transport modes is of no real use in comparing to private transport, it is interesting to compare the differences in Table 3 across cities for the same mode.

Buses: Examining buses first, we see that Jönköping and American city buses consume 32.1 and 31.3 MJ/km, respectively. At the lower end, we find Umeå and Uppsala have only 12.0 and 13.3 MJ/km, respectively, while Freiburg consumes 17.9 MJ/km, and European cities, overall, show 18.8 MJ/km, quite like the average for all Swedish cities of 18.0 MJ/km. The larger cities in Sweden consume 17.4 MJ/km, while buses in the smaller cities consume 18.5 MJ/km or quite close to the European average. In 2005–2006, the "world average" for buses, based on this large sample of global cities, was 23.1 MJ/km.

Trams and light rail (LRT): These rail modes represent very similar technologies, and their differentiation is somewhat artificial. In the Swedish cities and Freiburg, all such modes have been classed as LRT, and they only exist in Stockholm, Göteborg, Linköping and Freiburg. In the global sample from 2005, trams and LRT exist in at least some of the cities in all regional groupings. For the purposes of comparison with the Swedish cities and Freiburg, the average for the other regional groupings of tram and LRT were used (i.e., American, 17.3 MJ/km; Australian, 10.8 MJ/km; Canadian, 16.2 MJ/km; European, 13.3 MJ/km; Asian, 9.8 MJ/km; and with a global average of 13.8 MJ/km).

The data reveal the Swedish cities to be well within the normal range of energy use by these modes (11.9 MJ/km) and closest to the Australian cities, while Freiburg (13.0 MJ/km) is very close to the European average (13.3 MJ/km) and the global average from 2005–2006 (13.8 MJ/km). Swedish cities are within a relatively tight range in the three cities where LRT exists (10.5 to 14.0 MJ/km). Overall, tram/LRT systems have a range of about 10.0 to 17.0 MJ/km, depending on the age and type of system.

Metros: Metro systems are mostly underground systems and tend to operate in the denser inner parts of metro regions (e.g., the Paris metro in the Ville de Paris at the center of the Paris region known as the Île de France). In Sweden, a metro only exists in Stockholm (tunnelbana), while in the global sample, metros exist in at least some cities in all regional groupings. Stockholm's energy use per vehicle kilometer (wagon kilometer not train kilometer) is 7.8 MJ/km, which is reasonably close to the European average of 9.3 MJ/km, but significantly less than in all other groups of cities (a range of 13.5 MJ/km in Canadian cities to 22.6 MJ/km in Australian cities and a global average of 12.7 MJ/km).

Suburban rail: This rail mode covers the rail systems that operate over longer distances and include both underground sections in denser parts of cities and a lot of aboveground operations in lower-density suburban-type environments. These include the S-Bahn and regional rail systems in Germany, the RER suburban rail services throughout the Île de France and the regional rail operations that exist in all ten Swedish cities in this paper, as well as in Freiburg. Rolling stock is mostly bigger and heavier, including double-decker wagons, and train speeds are much higher than those of metro systems (see Section 4). In this mode, there is a very wide range of vehicular energy use per kilometer, depending on the type of trains, their fuel (diesel services are much higher in energy use than electric services), their age, number of wagons, their size, weight, passenger loadings and operating speeds.

All Swedish suburban train services are longer-distance regional rail lines which operate at high average speeds. Their energy use is, on average, 22.6 MJ/km, which is like the global average of 23.9 MJ/km, but with a big difference between the larger cities (31.8 MJ/km) and the smaller cities (13.5 MJ/km). Freiburg averages 19.0 MJ/km. Globally, there are also huge differences with a range of 11.9 MJ/km in the all-electric Australian cities, up to 50.4 MJ/km in the USA with a mixture of diesel and electric, mostly commuter rail style services. Canadian systems are similar, averaging a relatively high 43.0 MJ/km, whereas the European and Asian systems are virtually all electric and average only 15.6 and 14.8 MJ/km, respectively. The range in energy use per vehicle kilometer in the ten Swedish cities is from 5.0 MJ/km in Örebro up to 38.3 MJ/km in Stockholm.

Ferries: These modes only exist in Stockholm and Göteborg in the Swedish sample, but all the other regional groupings of cities have at least some ferry services. Ferries are very high in their vehicular energy use, a main factor being the very large frictional forces that must be overcome to ply through water and the speeds at which operate. Naturally, the size of vessels, which varies hugely around the world, is also a key determinant of energy use. Swedish cities average 236.9 MJ/km, with not much difference between the two cities (230.4 and 243.4 MJ/km). The global average was 358.8 MJ/km, with a massive range from 140.7 MJ/km for the ferries in Perth, Brisbane and Sydney (European cities were virtually identical at 141 MJ/km), up to 1073.3 MJ/km for ferries in US cities

(only New York and San Francisco). The Asian cities (Hong Kong only) are also very high, with many large and heavily loaded double-decker ferries in operation.
