**1. Introduction**

Until the 1973–1974 Arab oil embargo from October 1973 to March 1974, (the first global oil crisis) the use of energy in transport was not seriously on any academic or policy agendas. When OPEC (the Organization of Arab Petroleum Exporting Countries) declared an embargo on oil exports to countries deemed supportive of Israel during the 1973 Yom Kippur war with Egypt, the global price of oil essentially quadrupled 'overnight', from about \$US3 per barrel to \$12 per barrel [1,2]. Suddenly the world realized how vulnerable it is to events in the Middle East which affect the production and export of oil and its price. This stirred a spate of interest in this topic e.g., [3,4] and led to a growing concern about how to reduce dependence on oil in transport, particularly imported oil, and especially in cities [5,6]. The 1973–1974 oil crisis played out very differently in different cities. Dutch cities (The Netherlands was included in the embargo) adapted well to the crisis, since they were compact places which relied heavily on walking and cycling anyway, while the automobile cities in the USA experienced significant societal disruption as people scrambled to fill their very gas guzzling cars [7].

The world was again rudely awakened to this issue in the subsequent Iranian oil crisis in 1979 [8] caused by the Iranian Revolution. Iran's daily oil production of 6.05 million barrels per day, of which about five million barrels were exported to supply about 10% of the non-communist world's daily needs, was thrown into chaos. This event again brought into focus the dire situation of the world in regard to its political vulnerability to oil supply and its sometimes-volatile pricing. The need to reduce petroleum consumption and its dependence on Middle Eastern sources was firmly on the table. Unlike stationary uses of oil, such as for heating homes and in industry, which can be relatively quickly swapped to other energy sources, the petrol and diesel derived from oil and used in transport is a difficult issue because these liquid fossil fuels as a source of energy are particularly suited to mobile uses due to their high-energy density and thus long range of vehicular travel on one fill, ease of distribution, and convenient, compact and safe storage inside a vehicle. Conventional oil cannot be easily substituted, as exemplified over the last years with efforts to produce oil from non-conventional sources and electric cars on a larger scale. Oil from oil shale, tar sands and coal, as well as from other fuels such as ethanol and methanol, have all proved to be difficult. They have been too expensive relative to conventional oil, have had a poor net energy return and have had large environmental impacts from mining and other problems [9].

Despite the above history and the current urgency of CO2 reduction from carbon-based fuels, liquid fossil fuel consumption in passenger transport throughout the world has continued to rise in the relatively wealthy cities in the West and in currently less wealthy, but rapidly industrializing and motorizing cities elsewhere, such as in China, India and Brazil [10]. The sheer size of the population in such countries and others, as well as the growing environmental problems in cities from, for example, air pollution, has made it even more critical today to try to reduce transport energy use and especially dependence on oil as the major source of transport fuels. Rising living standards and incomes and increasing car ownership and use, especially in such populous countries mentioned above and the continued profligate use of transport energy in North American and Australian cities, for example, make it difficult to reduce global oil demand in the transport sector. This is especially so when there are, for the most part, still few disincentives to car ownership and use in cities and insufficient investment in alternatives to motorized private transport, such as quality public transport and good walking and cycling conditions [10].

Of course, over time there are numerous fluctuations in this general upward trend of transport demand and energy use in transport as economies fluctuate along with the demand for and price of oil. The West Texas Intermediate (WTI) or New York Mercantile Exchange (NYMEX) oil price per barrel (in US dollars) between April 2008 and August 2008 was above \$US135, peaking in June 2008 at \$164, but by September 2008 and the major onset of the Global Financial Crisis, the oil price dropped to \$118 per barrel and proceeded rapidly downward to \$50 per barrel by January 2009, as demand fell away. Oil prices did recover to some extent after this as the global economy and demand again picked up, and in December 2019, oil was \$61 per barrel [11]. The global COVID-19 pandemic, however, saw passenger transport demand in cities basically collapse, and the price of oil in April 2020 had plummeted to just \$19 per barrel.

Regardless of these perturbations, the issue of transport energy use in cities is still of major concern. A focus of discussion since the mid-1990s has been the geopolitical implications of oil reserves concentrated in the Middle East and the issue of "peak oil" when half the world's known oil reserves have been used and the production curve heads downward [12,13]. Although "peak oil" is disputed e.g., [14], the realities of war in the Middle East mostly focused on maintaining oil security for the United States (Gulf War in 1990–1991 and the Iraq War from 2003 to 2011) remain, as does the critical need to engage with the idea of a post-petroleum future.

Since the mid-1970s, much has been published about transport energy use in cities, and the author's own work has had a focus on growing the evidence about the best ways to reduce energy use in urban passenger transport systems through reducing automobile dependence and taking advantage of the different energy consumption rates of urban transport modes [15–17].

This paper continues in this tradition with a special focus on ten Swedish cities, plus Freiburg im Breisgau in Germany, as a benchmark small city known for its sustainable transport performance [18,19]. Sweden established a national research and education think tank on public transport called K2 (The Swedish National Centre for Research and Education on Public Transport), with the express aim of improving public transport's role throughout Sweden and shifting modal share toward public transport. As part of the author's research in K2, this paper reports on detailed comparisons of many aspects of land use, transport and other transport-related factors in ten Swedish cities, including the energy consumption of each passenger transport mode and attempts to answer the following three research questions about private passenger transport energy use in Swedish cities:

