Geotab made a rough estimate of the quietest route in each state, based on average traffic. The methodology:
To find the quietest road in each US state, we gathered the latest available (2015) traffic count data from the Highway Performance Monitoring System. Quietness was calculated as the annual average daily traffic (AADT, measured in # of vehicles), and routes with the lowest AADT in each state were deemed the quietest. Lengths of routes were gathered from local transport authorities in each state. The data covers Interstates, US Routes, and State Routes over 10 miles long.
I feel like they should’ve normalized by length of route, especially since they had it already. But hey, I’m always down for some peace and quiet.