Figure 2: Calculation domain for double fences case: 3D view (left), and x-z cross section (right). Wind at the upstream boundary at x=0 m is shown schematically on the right panel; velocity is 1.0 m s-1 at 2 m high. In the single fence case only one fence is remained at the downstream side. Road width is 10 m. Each fence is 4 m high and 10 cm thick.