My understanding is that the vast majority of road noise is caused by vehicles outfitted with non-standard tires. Where I live, 90% of the road noise is caused by lifted trucks using massive off-road tires on local roads and highways. It isn’t clear if this against the law all over the country, but in various US states, the police will issue tickets. There are several employees of local businesses who commute nearby and wake up the neighborhood when they go to work and when they return with the sound of their huge off-road tires getting on and off the highway. I’ve driven next to them on the highway several times and the noise is deafening. I can’t see how this is allowed. Next time I drive past them, I will run the NIOSH SLM app and record the decibels.