Why are there so many different types of bridges on the road network?
The ages of the bridges on the trunk road network span a period of at least 100 years, some of them having been built many decades before the trunk road network was designated. Methods of design and materials have changed and improved dramatically over that period and modern designs tend to be more efficient in both labour and materials. The most efficient type of structure at each location will also vary, depending on the loads to be carried and the obstacle to be crossed.
