Southbound traffic on Interstate Five was snarled Tuesday afternoon for multiple reasons. Shortly after One O'clock something began starting spot fires along the side of the freeway. The first of them apparently started in the Knighton Road area and they stretched south all the way as far as the Corning area. Cal-Fire engines chasing those fires caused some traffic congestion. That problem was compounded when a box truck and a big rig collided near Hooker Creek Road at around 4 O'clock. Traffic then slowed nearly to a stop and backed up well into Shasta County.