Slow US highways
Again Small/Smaller Euro cars are often good at this, as freeway speed in Europe are generally higher.
70mph UK, up to 80-90mph on some German autobahn's.
As mentioned above, why does anyone really think road/geography/vehicles is the US and Canada is really any different from Europe. Smaller cars/engines/diesel/efficiency in Europe are common - no reason why the benefits can;t apply to the US too.