Traffic on Southbound Interstate 5 was backed up for miles following a big rig accident Tuesday morning. The accident happened just after 9AM when the driver of the semi apparently drifted onto the shoulder, then tried to get back onto the pavement and flipped, hitting another vehicle in the construction zone near the riverside on-ramp. Even though one lane was reopened at times, traffic was backed up as far as the South Bonnyview Overcrossing. It took several hours to return to normal.