Complex sentence: Instead of the traffic rate increasing to 1985, it peaked in 1978 and then proceeded to decrease--attributed to the slowdown in Japan's economy since the first oil crisis in 1973, and to advances made in air transport facilities and longer-range sea transport.
Split into simpler sentences: Instead of the traffic rate increasing as predicted to a peak in 1985, it peaked earlier in 1978 and then proceeded to decrease. The decrease was attributed to the slowdown in Japan's economy since the first oil crisis in 1973, and to advances made in air transport facilities and longer-range sea transport.