Socioeconomic evaluation of the Grand Sud-Ouest Project (GPSO) — SNCF Réseau

The Major Southwest Project is an essential link in the European high-speed network, aimed at improve connections between Paris, Bordeaux, Toulouse and Spain, while strengthening the attractiveness and competitiveness of south-western France.

Explain intervened to make thecomprehensive socioeconomic assessment of the project within the framework of regulatory requirements related to the Declaration of Public Utility (DUP) and European cost-benefit analysis obligations.

The study mobilized a robust and innovative approach, combining:

• La rail demand modeling based on multimodal models calibrated at national and regional levels;
• The analysis of Modal reports (plane, car, coach) induced by the commissioning of new lines;
• The estimate of socioeconomic benefits : time savings, operational savings, reduction of CO₂ emissions and accidents, effects on congestion and travel comfort;
• La monetary valuation of environmental externalities and the measurement of economic benefits for the territories served.

Explain also provided the updating the evaluation framework according to the latest recommendations of the General Commission for Strategy and Foresight (CGSP) and CEREMA, guaranteeing the methodological compliance of the file.

The analysis work resulted in a reasoned summary of socio-economic performance indicators, making it possible to justify the viability of the project and to demonstrate its collective long-term profitability.

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The mission aimed to provide SNCF Réseau and to the State a complete and updated assessment of the socio-economic value of the project, integrating the dimensions:

• Economical : financial and collective profitability, value creation, knock-on effects on territories;
• Environmental : carbon balance, impact on air quality and energy consumption;
• Societal : accessibility, regional attractiveness, contribution to territorial cohesion;
• Foresight : robustness of the results in the face of scenarios of evolution of demand and the energy context.

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The study conducted by Explain allowed SNCF Réseau to have a rigorous and documented analysis, supporting the decision-making process and the presentation of the project to public and financial authorities.The results confirmed the added value of GPSO in terms of environmental performance and the dynamization of territories in the southwest. By mobilizing cutting-edge modeling tools and a strategic reading of impacts, Explain contributed to strengthen the credibility and transparency of public evaluation major infrastructure projects.

Explain provides major added value through its recognized expertise in railway socio-economic studies. The mobilized team has a thorough and historical knowledge of the GPSO project, having participated in previous evaluations since the DUP file. Their approach guarantees methodological rigor, strict quality control procedures, an ability to interpret orders of magnitude, and a pedagogical approach to ensure the robustness and reliability of the results.