While there are many factors that may have a potential to influence traffic noise, traffic volume is the predominant factor. With that said, traffic is at its loudest when the traffic operates at Level of Service C. This is the condition of a stable flow of vehicles, at or near free flow in a lane, but lane changing and maneuverability may be challenging. During Level of Service C at 70 mph, there are approximately 1,500 vehicles per hour and per lane. When traffic volumes increase beyond Level of Service C, vehicle speeds decrease and lower the noise levels.
The correlation between traffic volumes and noise levels is a helpful tool for ADOT to determine the future noise levels based on current conditions. Generally, doubling the traffic may increase noise levels by 3 decibels (dBA), and an increase of 20- 25 percent in traffic volume may increase noise levels by 1 dBA.