Audition every sound, drag its parameters while listening, and save. The game uses your saved tuning. Use headphones: signals and cars are positioned in 3D (here: 3 tiles ahead of you, facing north).
Peak and RMS are in dBFS. “Target” is the peak this kind of sound should sit at; “Δ” is how far off it is. Peaks above −1 dB risk clipping (the game also has a limiter).