Reduce speed on the highway or expressway saves a lot over long distances.
Excessive speed increases proportionally your gas consumption and emissions. At 130kph, fuel consumption is 20% higher than 110kph. So you know what you have to do if you really want to save on long distances.
Beware, if you combine this speed reduction with high deceleration and powerful re-accelerations repeated, you may cancel the effect of reducing consumption and emissions.