Rimersburg area resident Clayton Rhodes has been injured in a traffic collsion in southwestern Clarion County.     And, State Police say that he was flown to Pittsburgh's U-P-M-C Presbyterian Hospital for treatment.     Rhodes had been driving a car on Route 68, in Madison Township.     And, he was following behind a tractor-trailer, which was operated by Jeffery Toy of Curwensville.     The big truck had come to a stop, on Route 68, in the area of the Rimersburg V-F-W post.     However, Clayton Rhodes failed to notice that the tractor-trailer had halted on the highway.     So, the Rhodes car then slammed into   the rear of the big truck at high speed.     This wreck took place shortly after one Monday afternoon.