I notices that fastest route is chosen.
I always watch for alternatives if there is a similar time but shorter version.
Wery ofter is similar time (for example 20minutes faster vis highway, 23 minutes via road), but via high way is 30 km, via normal road is 15km. Difference in consumprion is huge, difference in time is acceptable, even if I calculate the price of my time.

If you calculate best way based on "price", optimal way will be better.

Solution: calculate price of people time (for example 10USD for an hour) and 0,1 USD for one kilometer. Best price is the best way.
Great would be is the user could change these values.

Many thanks
Petr