Traffic Collision and Visibility Issues, Fresno County, CA


On October 16, 2004, a traffic collision occurred on California Avenue, 100 feet east of Bryan Avenue in Fresno County. At the time of the collision there was large cloud of dust covering the roadway that was caused by farm equipment used to harvest an almond orchard. The cloud of dust obscured the vision of the parties involved in this traffic collision. At the time of the collision, two almond-harvesting equipments (Source 1 and Source 2) were in operation.

EnviroComp's Role

We were retained by the attorneys representing one of the two almond-harvesting companies and asked to analyze the dynamics of the accident, understand the meteorological conditions at the time of the accident, and simulate the plumes of dust originating from the two almond-harvesting activities.

Our technical work included a visit to the site, collection of pictures, a literature review of the characteristics of almond-harvesting equipment (to calculate the amount of generated dust), dispersion modeling of dust, and visualization of the results. The area and location of the accident is presented in the figure below (Figure 1).

Our work first included the simulation of the dust concentration created by the two sources. This figure (Figure 2) presents the concentration impact of Source 1, while this figure (Figure 3) shows the concentration impact of Source 2. It should be noted that the plume from Source 2 generates much lower concentrations but a larger horizontal impact.

To visualize the actual visual impact of the plume on the drivers, we performed optical calculations for the dust plumes. Starting from a clear picture (Figure 4) of the drivers' view, we calculated the distance from the viewer for every pixel of the image. Then, by using the integral dust concentration in every pixel, we were able to generate the dust cloud extinction array, transmittance of dust clouds, radiances from target and sky above target, and contrasts. The results of this visibility modeling effort are presented in Figure 4 (no dust), and the subsequent figures with the impact of Source 1 (Figure 5), and the impact of Source 2 (Figure 6). We were able to conclude and visually demonstrate that, for all practical purposes, only Source 1 was responsible for visibility impairment.


Figure 1 Figure 2 Figure 3 Figure 4
Figure 5 Figure 6