Energy consumption vs time saving

There is a construction site at the feeway exit for my work place. Because of that, it takes about ten minutes more to commute. That triggered me to drive along the other site of lake Zug. It is the shorter route. But since it is a small road that goes through all the villages, it usually takes about ten minutes longer. What is more interesting, is the energy consumption.
On the freeway route the car usually consumes between 15 and 23 kWh per daily commute. The actual value depends mainly on temperature and weather conditions. The highest consumption values are with freezing temperatures and snow storms. This results in bad aero-dynamics and high rolling resistance combined with energy used for heating the cabin.
On the alternative route the car only consumed about 11kWh the other day. That was with moderate temperature and a short part of freeway. And this was still with winter tires, which usually lead to higher consumption.
The massive difference is not explained by the shorter distance, but by the slower speed. Hence by driving the shorter route, I could reduce the energy cost per daily commute from an average CHF 2.7 to CHF 1.7 but is this worth enlarging the commute from 2×30 to 2×40 minutes? Not really!
Oh and BTW, the daily commute by train would be CHF 25 and take on the order of 2×50 minutes.