The scatter plot below shows the average traffic volume and average vehicle speed on a certain freeway for 50 days in 1999. Which statement best describes the relationship between average traffic volume and average vehicle speed shown on the scatter plot?

As traffic volume increases, vehicle speed increases at first, then decreases.
As traffic volume increases, vehicle speed decreases at first, then increases.
As traffic volume increases, vehicle speed increases.
As traffic volume increases, vehicle speed decreases