In recent years, infrastructure investment policies have undergone a profound transformation, driven by European initiatives such as NextGenerationEU, TEN-T, and the Green Deal. These instruments not only call for a new design paradigm for infrastructure but also impose stringent requirements for reducing environmental impacts. However, this evolving framework has led to the development of high-performance infrastructure projects, which risk further extending already lengthy construction timelines. The academic literature has extensively focused on the economic effects of infrastructure on local territories, particularly in the post-construction phase, as well as on how the availability of transport networks influences regional dynamics. In Italy, these studies are usually part of cost-benefit analyses used to justify public investments and guide the Triennial Public Works Programme. Yet, the socio-economic effects during construction are rarely explored, despite the fact that the prolonged presence of workers and construction activities can activate significant local dynamics. This article aims to explore the relationship between demographic evolution and the presence of construction sites as a factor in local economic development. It also examines how local administrations have included construction activities in urban planning, especially regarding land use changes. The analysis is based on the case study of the Terzo Valico dei Giovi (TV), a high-speed railway line connecting Genoa and Tortona, which since 2012 has involved over 5,000 workers distributed across six base camps located between the regions of Liguria and Piedmont.