Traffic was stopped for just over 30 minutes last evening on westbound Interstate 94 at the Smiths Creek Road overpass in Kimball Township as crews extinguished a car fire.   It is reported that the female driver of the car was experiencing car trouble and pulled over underneath the overpass when her engine started smoking just before 6:30 p.m. Sunday.   By the time firefighters arrived on scene, the car was fully engulfed in flames and crews remained on scene until just shortly after 7 p.m. Neither the woman nor her child passenger was injured in the incident and the cause of the fire is unknown.