So we want to know how much greater is the intensity of noise if the decibel level of traffic goes from 40 to 60 dB. So the formula for intensity in decibels is: I(dB)=10log(I/I0) where I is the intensity, I0 is 10^-12 W/m^2 and I(dB) is the intensity in decibels. To get intensity in W/m^2 we need to invert the equation to get I: I=I0*10^(I(dB)/10). So I1=I0*10^(40/10)=I0*10^4=(10^-12)*10^4=10^-8. I2=I0*10^(60/10)=10^-6. So I2-I1=9.9*10^-7 W/m^2 is how much the intensity is greater when the traffic went from 40 to 60 dB.
