The Norwegian Public Roads Administration has applied ecological speed limits of 60 km/h on selected sections, as a measure to ensure better air quality and also to reduce the number of road accidents.

Due to winter measures taken against slippery surfaces, those with health problems caused by road dust are particularly at risk.

The reduced vehicle speed is effective from November 1st until the beginning of May 2024, when the spring road cleaning is completed.

The winter speed restriction will cover the sections:
-Rv 4 Sinsen-Grorud
-Ring 3 Ryen-Granfosstunnelen
-E18 Hjortnes-Lysaker (applies on weekdays from 06:00-22:00)
-Rv 163 Østre Aker vei Økern-Stovner

On the E6 in Trondheim, variable speed limit signs have been installed, allowing for the reduction of speed when necessary.
The measure was tested in 2019 and showed that a reduced speed limit decreased the levels of particulate matter by 21 – 25 percent.

source:
https://www.vegvesen.no/fag/fokusomrader/klima-miljo-og-omgivelser/luftforurensning/miljofartsgrense/