In 2011, SDDOT measured the amount of traffic on its highways in National Highway System, a system of highways important to the nation's defense, economy, and mobility.
SDDOT measured the amount of traffic on its highways in National Highway System. This was in 2011. SDDOT measured the amount of traffic on its highways in a system of highways important to the nation's defense. This was in 2011. SDDOT measured the amount of traffic on its highways in economy. This was in 2011. SDDOT measured the amount of traffic on its highways in mobility. This was in 2011.