I started thinking about the stereotype of the large american car, which I'm guessing is a result of rather spacious roadways in the US compared to many other countries around the world.
Is this simply a matter of geography? Or was there something else behind the development of wide US roadways and wide US automobiles? Does it have anything to do with US cities and infrastructure still being developed as the age of the automobile was starting? (compared to say, tightly knit communities in Italy/Japan?)
Well for roads it is because a lot of our towns were made after the invention and acceptance of the automobile. Although my town was around since the 17xxs so we have extremely narrow roads in some places. Some so narrow a garbage truck cannot get through. Highways are probably the same in the US and elsewhere.
As for cars. A lot of it comes down to fuel prices, and how new cars are taxed. Cars in much of the world are taxed based on engine size and the taxes are an incentive to get a small car. Not so in the US. This is also why automatic transmissions are popular in the US.
You see we could easily afford the big powerful engines. And in the early days automatic transmissions took a tremendous amount of power just to operate. It couldn't be done with 40 HP four cylinders.
Do you mean width of lanes or number of lanes?
For most of the 20th century, the United States has had siginficantly lower gasoline prices than many other industrialized nations. This page has a list of nominal and real gasoline prices in the United States since 1949: http://www.eia.gov/totalenergy/data/annual/showtext.cfm?t=ptb0524
Notice that according to the above analysis, gasoline prices in United States had generally been below $3/gallon in inflation-adjusting real terms for most of the last 50+ years.
For our friends across the pond, that means that for most of the last 50+ years, Americans have paid less than the equivalent of 0.79 euros per liter for ordinary petrol, when taking exchange rates and inflation to account.
I'm having a somewhat harder time finding historical fuel price data for Western and Northern Europe pre-Eurozone because of vagaries of exchange rates and because I really only speak English. However, here's another page form the EIA: http://www.eia.gov/countries/prices/gasolinewithtax.cfm
This page shows the last 20 years or so of gasoline prices across Western Europe as annual averages, converted to dollars per gallon, with an attempt for take variable tax rates into account. Explaination of the exact methododology is in a link at the bottom of the page. Anyway, this page shows that, generally speaking, consumers in European OECD members have usually paid around twice as much as American consumers for gasoline.
Taken in aggregate, this suggests that the marginal costs of owning car in the United States has consistently been lower than in Europe for at least the last 20 years and probably much longer than that. So many more people own cars in the United States, because the cost of doing so is lower, at least in the short to medium-term. This has encouraged widespread adoption of automobiles even by fairly working-class members of society.
Compounding this, many of the today-largers metro areas in the United States, such as Dallas, Houston, Atlanta, Los Angeles, and most of Florida, underwent their major phases of urbanziation and economic growth in the post-1920 era when infrasturcture devevlopment was very car-centric. This is starting to change, very slowly, but only in a few small areas where it's possible to achive the right mix density, public-transportaion, and public spaces, to make create an urban fabric that is targeted towards the needs of pedestrians and cylcists, rather than automobile drivers. That last bit is probably a little too editorial, but it's all based on ideas discussed in Jane Jacobs's The Death and Life of the Great American Cities..
Does that help answer your questions at all?
Are you really sure this underlying assumption is true?