This publication outlines the development of a modular precast concrete bridge system. This new system provides designers with a concrete solution for medium span bridges that can be used for the majority of bridge locations. The modular system incorporates easily transportable precast concrete shell units that support and combine compositely with the post-tensioned, in-situ concrete core. Guidance includes an introduction to the system followed by structural details, construction options and example costs. Scheme drawings and construction programmes for case study examples are also provided.