They use less fuel but they are more expensive and they also produce more polluting particles than petrol cars, and with diesel fuel now being as expensive, sometimes more expensive than petrol, I'm not sure why anyone would want to buy one these days.

Diesel still has a proper spot in hauling truck use for trailers, etc. With that said, I see a future where more Semi's are CNG or Hybrid of Electric motor driven with a gas or CNG Generator.

 

Technology has moved to allowing us to finally move beyond old standards.

On a Volkswagen Beetle TDi 2013, it is a difference between 32 MPG and 46 MPG.

On a Volkswagen Beetle TDi 2013, it is a difference between 32 MPG and 46 MPG.

 

Highway or combined?

Well I have posted mathematics in my thread about the car.  Those figures are for summer blend fuel, running my former commute.

I don't see the average sedan ever being diesel, there are going to be the odd one or two that do but most will be petrol until we find an alternative fuel source. Trucks on the other hand often run on diesel and that likewise isn't likely to change in the near future. Though I see Trucks changing far sooner than cars. 

Kenworth and Peterbilt Assembly plants in Renton Washington now have dedicated lines producing CNG Semi's. I believe that more cities will push to remove diesels from the road of the inner city streets and require either electric or CNG. Many cities on the west coast have plans to be fully alternative fuel / powertrains by 2018 with no more diesels.

 

I know Buffet is pushing to convert the trains to CNG, Long Haul trucks will be a much slower change.