Road infrastructure improvement is an important factor in supporting community mobility and regional economic development. This study discusses the Detailed Engineering Design (DED) planning for the Bulumargi – Datinawong Road Reconstruction, Lamongan Regency, which aims to produce a technical design that meets Indonesian road planning standards. The research methods include field surveys, geometric, traffic, and subgrade data collection, and technical analysis using Bina Marga guidelines. The results show that the existing road conditions require structural and geometric improvements to accommodate current and projected traffic volumes. The resulting DED planning includes geometric design, pavement thickness, drainage, and budget plans. The conclusion of this study is that the reconstruction of the Bulumargi – Datinawong road can increase traffic service capacity, extend the pavement life, and support inter-regional connectivity in Lamongan Regency.