This paper presents a transmission need analysis for the Eastern Interconnection (EI) using a coordinated technical approach consisting of system reliability assessment (SRA) and production cost simulation (PCS). As North American Transmission Systems are being evolved with increasing levels of renewable energy resources such as wind, solar, storage, biomass, hydro, etc., maintaining grid reliability and managing transmission congestion cost are becoming increasingly challenging. It also poses complexity and challenges in technical and economic planning of the transmission grid. The coordinated SRA and PCS were conducted to assess transmission reliability and congestion for the interconnected grids of the EI in a 10-year planning horizon. The paper discusses new automation tools and models developed for such assessment including case studies showing the applicability of the coordinated methodology and developed models.