Traffic impact fees are a one-time payment made by developers to help pay for their "fair share" of the cost to provide the roads necessary to serve their development. Typically these fees are collected by the appropriate city, county or state agency (usually Caltrans) when permits are issued. Periodically studies are done to evaluate the future development growth expected in a specific area or corridor, the costs to provide the necessary infrastructure as development happens and the appropriate fee to be charged. SRTA has led three regional studies over the past decade. These include: