Motor carrier accident investigation report. 68-1. Carlsbad Cavern Coaches, accident, Dec. 16, 1967, Salt Flat, Tex., Western Greyhound Lines, accident Jan. 2, 1968, Oakridge, Oreg., Eastern Greyhound Lines, accident, Jan. 4, 1968, Moscow, Pa., Midwest Buslines, Inc., accident, Jan. 9, 1968, Henderson, Tex.