*Approaches for Noise Barrier Effectiveness Evaluation Based on* In Situ *"Insertion Loss"… DOI: http://dx.doi.org/10.5772/intechopen.104397*

equivalence conditions include wind, temperature, humidity, and cloud cover. In case of strong winds, "before" and "after" measurements should be avoided.

The factors to be considered in the determination of the measurement sites and procedures are briefly described below:

## *3.1.1 Noise emission source*

The ISO standard recommends the traffic itself as the sound source for the "before" and "after" measurements. Using traffic noise signal has the advantage of measuring the signal which is wanted to evaluate. However, the fluctuations in traffic may affect the accuracy of the results, so that the measurement period must be taken into consideration.
