The Europeans (most governments) have chosen to collect revenue & encourage conservation by regulating fuel prices via their tax system. I cannot testify as to details, but the high fuel prices do work to encourage use of the most efficient choices for transport. They have very good rail systems and city mass transit which means that lower income workers seldom feel the need for cars, or chose small cars and motorbikes (or just bicycles - hence the Tour de France). Thermodynamically (I am a Physicist) the compression ratio is the primary factor for efficiency (establishes a ceiling) so diesel, needing the high compression, is the most energy efficient choice. The added stress also requires a more sturdy engine, but diesels last a long time. Engines with spark plugs cannot reach the high compression of a diesel without special/expensive fuel.
In the US, we decided on controlling POLLUTION by direct regulation of emissions, not energy use. The result is a complex engineering problem that puts diesel engines at a disadvantage because with the dirty diesel fuel (high sulfur) and high compression (high flame temp) diesels generate more Sulfur dioxide and Nitrogen Oxides which are major causes of acid rain.
Now the fuel is cleaner, (reducing Sulfur) and new exhaust pipe engineering reduces Nitrogen oxides, Also new injector systems reduce noise.
In short, the europeans got a similar reduction in pollution by a different (better I think) approach which permitted them to reduce emissions by reducing consumption.
They had to invest heavily in infrastructure and car ownership costs though, which is now beginning to pay off nicely. They had to use a different solution because they were not so resource rich as we were, and their choice made very good economic sense after WW 2.