Complex sentence: Originally designed as a joint railway and road bridge the bridge consisted on a center rail line with 12 foot extensions on each side for traffic, these remained in use until 1960 when the nearby Diefenbaker Bridge opened.
Split into simpler sentences: Originally designed as a joint railway and road bridge the bridge consisted of a centre rail line with extensions on each side for traffic. These traffic lanes remained in use until 1960 when the nearby Diefenbaker Bridge opened.