The French National Assembly established the basis for the building of a metropolitan RER network in 10 major cities, excluding Île-de-France, within ten years.

Defined as a “single ticket”, the proposed law will allow the Société du Grand Paris (SGP) the development of future metropolitan RERs known as "metropolitan regional express services" (Serm).

This followed Emanuel Macron, the head of state, reintroducing the notion of building metropolitan regional express networks (RER) in 10 major cities at the end of November 2022.

The project involves the opening of certain territories along with the decarbonisation of transport.

According to the French association, Objectif RER métropolitains, the project will “open up our daily mobility areas” and “pave the way for the ecological transformation of our territories”.

Serm initiatives will primarily attempt to improve the “quality of everyday transportation”, particularly by providing more frequent and dependable services to peri-urban regions, as well as reducing air pollution.

The Prime Minister, Elizabeth Borne, confirmed the project in February 2023, following a report by the Infrastructure Orientation Council and the unveiling of a €100bn train construction plan to 2040.

This project follows the government's regional transport plan which aims to provide €9bn in funding across 2023-2027. This saw the Minister for Transport, Clément Beaune travelling across the region signing State-region plan contracts.