This paper presents the analysis and results from radio frequency interference (RFI) monitoring along main highways in Norway. The work started with an initial two months monitoring campaign in 2013, followed by a few shorter monitoring campaigns up through 2017. From January 2018 the system has been monitoring continuously, but the presented results cover only data up to the end of 2019. The extracted trend data show that the number of intentional jammers have increased from 2013 and up to 2018, but indicate a significant reduction in 2019. One potential reason for the reduction in 2019 can be that GPS jammers had a rising interest in the Norwegian media in the first quarter of 2019, leading to increased public awareness of the illegality of jamming and the potential to be caught if using jammers. The detections, including both intentional and non-intentional interference, are relatively equally distributed among the different vehicles, however the detections that are likely to originate from intentional GNSS jammers are mainly found in trucks and vans, often marked with a company logo.