Future4West, as the project is now called, aims to construct a mass transit system with four rail lines to Bath, Bristol Airport, Emersons Green and Cribbs Causeway, some of which would go underground.

https://www.newcivilengineer.com/latest/tunnelling-work-for-planned-bristol-underground-would-be-relatively-easy-22-03-2023/?utm_medium=email&utm_content=_J9kCdgw3OHzVqMW4RUTUUlufZwcbY9jNLW6W6VcSjPnv2EgEbUnLuObh2kffS9O&idU=3