Caltrans Online Training-Highway Noise Measurements and Instrumentation

First we'll define the relevant wind classes. There are three wind classes. In the upwind class, the vector winds range from -1 to -5 meters per second -in other words, the crosswind component blows from the receiver to the source. The "calm" wind class includes crosswind components from -1 to +1 meters per second. Note that the calm wind class does not necessarily mean that the wind speed is near zero. As an example, a wind blowing at a speed of 5 meters per second at an angle of 10 degrees with the highway would produce a crosswind vector of 0.9 meter per second. This would place the wind in the calm wind class, the same class as a 1-meter per-second wind blowing perpendicular to the highway. The downwind class crosswind vectors range from +1 to +5 meters per second. In the next slide, we'll take a look at the criteria for maximum allowable differences within a wind class.

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