A semi truck caught fire in the southbound lanes of I-405 Monday afternoon, making for a smoky mess during the initial part of the evening commute. Flames were seen spewing out the top of the truck as it sat just south of the NE 44th Street on ramp just before 3 p.m. Once firefighters got on the scene and started dousing the flames, smoke briefly poured over both sides of the freeway. Smoke was still pouring from the truck 20 minutes later and several-mile traffic backups had ensued.The fire was doused a short time later and the roadway opened just before 4:30 p.m.