<![CDATA[The Lambunu–Mepanga National Road in Central Sulawesi Province plays a strategic role as an interregional connector; however, its geometric conditions in the STA 15+500–21+500 segment do not fully meet Bina Marga standards. Survey results revealed 52 curves, several with radii of less than 30 meters for a design speed of 30 km/h, and vertical gradients reaching 15–16%, exceeding the maximum allowable limit of 10–12% for mountainous areas. This study aims to design safer and more efficient alternative horizontal and vertical alignments. The methodology includes field measurements, data processing using AutoDesk Civil 3D, and manual calculations based on Bina Marga guidelines. The alternative design resulted in 44 curves (4 Spiral–Circle–Spiral and 40 Full Circle) with increased radii and improved spacing between curves. For the vertical alignment, 32 curves were designed (15 convex and 17 concave), reducing the maximum gradient to 12%. These improvements enhance compliance with standards, improve sight distance, and reduce accident potential. The study recommends implementing the new design during the construction phase and conducting further studies on pavement design, drainage systems, and cost estimation to support optimal road performance and service life.]]>
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