Complex sentence: There was little traffic on Milton Road until the development of the outer western suburbs in the 1960s and 1970s and the opening of the Western Freeway which resulted in a considerable increase in traffic congestion.
Split into simpler sentences: There was little traffic on Milton Road until the development of the outer western suburbs in the 1960s and 1970s. The opening of the Western Freeway resulted in a considerable increase in traffic congestion.