This study explores the phenomenon of cost escalation in transport infrastructure, with a focus on large-scale projects in Scania, Sweden. Employing a mixed-method approach, the study integrates quantitative and qualitative data to assess both the extent of cost escalation and the underlying factors contibuting to them. The quantitative analysis inlcudes descritive statistics , t-test and scatter plot to based on a dataset of transport infrastrucutre projects, allowing comparisons between cost escalation trends in Scania and on a national level. Findings indicate that cost escalations are frequent and substantial challenge in Scanias transport infrastructure projects, aligning with patterns onserved nationally and internationally. The analysis shows both that road and rail projects subjected to budget escalation, with projects, with projects size and complexity emerging as notable factors influencing cost escalation. However, variations in cost escalation levels across project types and sizes suggest that cost perfomance is shaped by a combination of technical, organizational and contextual variables. 

The qualitative compontent, based on semi-structured interviews with stakeholder from public, private and consultancy sectors, provides deeper insights into the drivers behind cost escalation. Themes such as stakeholder misaligment, procuremnt challenges and governance complexity were identified as critical contributors to escalating costs. Interviewees highlighted the importance of early-stage coordination, transparent communication, and effective risk management to mitigate cost escalation. By combinding statistical analysis with stakeholders perspective, this study offers a comprehensive understanding of cost escalation in regional transport infrastructure. The study concludes with recommendations for enhancing cost control, including improved stakeholder collaboration, more robust planning practices and procurement strategies that better align incentives and responsibilities among the actor.