The proposal is one of six ‘big ideas’ that has been put forward for consultation by the county’s public sector umbrella group, Leadership Gloucestershire, and the University of Gloucestershire.
The ideas form part of the Gloucestershire 2050 project, which was launched on 1 February and aims to improve life in the county over the next 30 years.
According to the Gloucestershire 2050 consultation website: "Gloucestershire’s two main urban centres – Gloucester with its cathedral city status and heritage, and Cheltenham with its spa town elegance – could grow and regenerate by developing a third centre connecting the two to create a ‘super city’."
A possible location for the third centre, the website says, could be on land alongside the A40 dual carriageway road between Cheltenham and Gloucester.
It adds: "Much of this land is currently designated as green belt, although has no specific landscape ‘value’ in terms of particular habitats, special features or protected flora/fauna. It is also suited to building development because it is relatively flat, has good access and a low risk of flooding."
The loss of green belt "could be compensated by the development of green corridors through the city into the surrounding countryside to ensure easy access to high quality natural environments", the consultation suggests.
It adds: "The new urban centre would be designed to keep and enhance the unique strengths of Gloucester and Cheltenham, so that the overall city has zones with individual character and identity, as in larger cities such as London.
"The re-developments and the new centre would be planned to address current and future key issues of the county, including the retention of young people, health, education, skills, employment, social cohesion, and sustainability."
The website says the new city could have a population of 520,000 – combining the existing populations of Gloucester, Cheltenham and parts of Tewkesbury Borough plus future planned growth - which would make it one of the top 10 UK cities in size.
Leadership Gloucestershire includes the leaders and chief executives of Gloucestershire County Council, the county’s six district councils, and the GFirst LEP.
Other ideas include restoring a crossing over the Severn River between Lydney and Sharpness and an expanded Cotswold Airport.
The Gloucestershire 2050 project aims to overcome key future challenges facing the county, the consultation website says, including an ageing population and a high proportion of young people aged between 18 and 30 leaving.
More details can be found here.