Spend time in any European city, and you'll quickly become used to two sounds.
One, is the constant buzz from thousands of mopeds, by far the quickest way of navigating the tight streets. The other is the subdued rattle of diesel engines.
While Europe has wholeheartedly embraced diesels, they've never really caught on in the U.S.--though the range of diesel models on offer is slowly increasing. And with hybrids becoming cheaper and regular gasoline cars more efficient, will diesel ever make sense as an alternative fuel?
Cost and availability
You won't have failed to notice the extra price of diesel over gasoline fuel when filling up your car.
Based on the most recent figures from the U.S. Energy Information Administration, a gallon of gasoline costs around $3.44 on average. A gallon of diesel will set you back $3.85. While $0.41 doesn't sound like a great deal, it's clearly going to be a cost that adds up, the more of it you use.
In Europe, this isn't the case in many territories. While diesel is around $0.50 per gallon more expensive in the U.K. than gasoline, the relatively high EU fuel economy figures and CO2 outputs are used to calculate annual registration taxes for cars. That means diesels can often be a hundred dollars or more cheaper each year to tax.
In other countries, such as France, diesel is as much as $0.80 a gallon cheaper than gas, which makes diesel cars significantly more cost-effective to run.
Unlike Europe, compared to gasoline filling stations, diesel pumps in the U.S are more sparsely distributed. So not only is diesel more expensive, but comparatively harder to find.
Cost of diesel vehicles - and cheaper, more efficient gasoline cars
While diesel fuel does cost more than gasoline, for many the cost can be offset by the extra economy of diesel engines. That $0.41 doesn't look so bad if you're going to be using far less of the fuel every time you travel.
In particular, diesels excel on the highway, where strong torque at low revs allows them to cruise using very little fuel without feeling underpowered.
Unfortunately, diesel cars also typically cost more to purchase in the first place. That means you really need to cover high mileage to make the most of them, to offset not only that extra cost of diesel over gas, but to justify the extra purchase price.
This would be easier to justify had regular gasoline cars not improved significantly in recent years. Now, it's quite possible to buy a relatively inexpensive car that does 40 mpg or more on the highway - in fact, we found ten of them for under $20,000.
The 2012 Volkswagen Jetta TDI, one of the more popular diesel models, has an MSRP of $22,775, and EPA highway economy of 42 mpg. The similarly sized 2012 Chevrolet Cruze Eco also manages 42 mpg highway according to EPA figures, but retails for only $19,175. At over $3,500 less and with cheaper fuel, you'd save money on every journey with the Chevy - and pay over the odds with the VW.
Clean air regulations
Though diesel vehicles have improved significantly in recent years thanks to particulate filters and urea injection, the gases emerging from their tailpipes still aren't as clean as those from the equivalent gasoline car.
With particularly tight regulations on clean air, particularly in states like California, that requires carmakers to spend even more ensuring their cars are clean enough - and that cost is pushed on to consumers.
Some manufacturers, knowing this, simply don't bother importing the wide range of diesels they sell elsewhere in the world, as the limited sales couldn't justify the extra cost.
Depending on what you're looking for in a car, diesels do offer a wide range of benefits. Heck, some recent diesels are even quite good fun to drive, certainly more so than many hybrids.
Performance is often relatively effortless, thanks to modern technology and turbocharging, and refinement is far beyond the image of the rattly, sooty diesel that many people hold - particularly with expensive, multi-cylinder units from BMW, or Mercedes-Benz.
Highway economy is also strong, and it's worth highlighting that although the VW Jetta TDI is quoted at only 42 mpg highway, several owners seem to be getting significantly more - figures into the 50s aren't unheard of.
However, people are more likely to use the EPA figures as a measuring stick, and on those numbers alone, diesel seems pointless.
A relative lack of pumps and the increased price when you get there, as well as high purchase prices, mean that as gasoline cars get ever more efficient (and hybrids increasingly affordable), the U.S. market for diesel cars could remain as limited as it is today.