[b112]

Hence the talk of aerodynamic design.

The numbers you quote don't show math, and even if they did, the math is different for each vehicle airflow.

Regardless, efficiency has many properties.

Time means more labour cost + cost of spending another day on the road, plus time not shipping something else.

I sometimes, in my car, drive from Quebec to California. It can take an extra day to make this drive, if I must drive slower due to weather, traffic, or construction.

EG 60mph vs 80mph average (yes, average without stops).

A little more fuel pales in comparison to these costs.

[timbit42]

Fuel is a lot more expensive in Europe, almost double.