Sils,
I love showing up at any petrol station in the USA and see the diesel fuel price is somewhere between 20-45 Cents (US) more than petrol. They give us the lame excuse that home heating oil is in demand or the demand for petrol and the refinery industry not being able to cope with both diesel and petrol demand that is the reason.
Our environmentist whacko's absolutely hate diesel engines....and the EPA demands eighteen wheelers pass a snap throttle test for "smoke" emissions (visible to the eye) and ignore the computerized engines ability to sense load, torque demand, rpm, gear position, road speed, exhaust gas temp, and thus vary engine fuel system performance to match the needs of the engine to obtain maximum mileage per gallon of fuel used and at the same time reduce emissions to a minimum.
As you drive behind a modern Big Truck and watch the exhaust stack...nothing but heat wave showing with no visible smoke....but the algorithm for cruise is not the same for idle or low power demand or high power demands.
It would appear to this cabbage headed dunce that if one can acheive 8 mpg with variable engine settings and only 5-6 mpg with a fixed computer setting, that the variable engine would put out less pollution than the other purely because of the reduction fuel consumption in the first place.
What we have here is the confluence of the failings of politics, science, and enviromental hooliganism. In the meanst while...we have not built a new refinery in 20 years, have not built any new Nuclear power plants in about the same time frame, and continue to add "anti-pollution" devices to the vehicles that only work to decrease the mileage rate of consumption and adding to the demand for crude oil. Alas that competition for oil, fires the desire for war and unrest.