Lowest speed highway

I was told I drive to slow on the highway and that is reason I failed my driving test. It was raining and drove 80 on 100 road. Did not see anything in books. Anyone can assist in answering that?

Which lane, left or right? Assuming it was 2 lanes in your direction.

Perhaps you were hogging traffic in a congested area?

The highway was clear. Just a few cars. Not holding up anyone. This was my first try and had about 100 hours practice.

Is there a rule about driving too slow on a highway?

Yes, there is a rule about that:

”16 § En förare får inte utan giltigt skäl köra med överdrivet låg hastighet”

Since there were not many cars, you had no reason to drive slowly. Why would you drive 80 if the highway was clear?

The lowest speed on a highway is by law 40 km/h. That does not mean you should drive exceedingly slow. I once drove down the highway when it started raining very intensely. Up to the point where you could barely see through the windshield properly. I slowed down heavily and I thought that was a good decision. One may want to slow down even in light rain if there are large pools of water on the highway, to avoid water planing.

Slowing down heavily in only light rain is probably not the right choice, given good visibilty and road grip.