The Clifton Suspension Bridge is a globally recognised icon of Britain’s proud, and continuing, infrastructure (or transportation) heritage. Established by an Act of Parliament in 1952, Clifton Suspension Bridge Charitable Trust’s mission is to maintain the bridge in perpetuity and to convey the bridge’s rich industrial heritage through educational services.
Completed in 1864, and now far exceeding the design life span of a modern bridge, the 159-year-old Clifton Suspension Bridge continues to provide an important and safe crossing over the spectacular Avon Gorge. Originally intended for horses, horse-drawn vehicles and pedestrians it now predominantly caters for light vehicles (such as cars) and cyclists. Its iconic status attracts hundreds of thousands of visitors annually who contribute millions of pounds to the city’s and wider region’s important tourist economy. The bridge is an easily appreciated example of the value of infrastructure to both society and the economy.
The bridge’s crossing and educational services alongside its operations and maintenance activities all generate carbon-equivalent emissions. To understand these, and to inform the Trust’s decisions, the Trust commissioned a carbon study by its consulting engineers, COWI.
PAS2080 is a standard for managing carbon in building and infrastructure. It looks at the whole value chain (the emissions caused by the supply and use of products) and aims to reduce carbon and cost through intelligent design, construction and application.
Drawing on the PAS2080 standard, COWI’s study analysed the contributions of embodied carbon (the amount of carbon emitted during construction), operational carbon (the energy used and consumed by the Trust), and user carbon (energy consumed by the approximately 2.5M vehicles crossing the bridge annually), revealing several valuable insights that support the importance and value of taking a whole-life, system-of-systems, perspective.
The results showed that the estimated embodied carbon of 6,700-7,000t CO2e is proportionately lower than for an equivalent modern suspension bridge. This largely reflects the high material and low labour costs of the mid-19th Century.
Today, the Trust’s estimated annual operational carbon is just 53t CO2e, whilst user carbon is 823t CO2e – equivalent to the emissions from 1179 homes. However, the bridge’s role in the wider city’s emissions generations should be taken into account. When the bridge is closed, the equivalent road route increases by approximately 1.8 miles. If the bridge were permanently closed, this could lead to an estimated c1,230t CO2e of extra annual emissions. The Trust’s policy of closing the bridge for maintenance during off-peak periods (09:30-15:30) saves c1.15t CO2e per day when compared with closures spanning peak periods.
The Trust is now better-informed and can monitor the effects of, for example, post-pandemic working patterns, the new Bristol Clean Air Zone, and electric vehicle take-up. This enables the Trust to make informed decisions in meeting its mission of extending the bridge’s sustainable, decarbonised life, and value to society. There are also significant lessons to be shared with the wider infrastructure community.