Ex-Ante Geometric Safety Evaluation of The Planned Sitinjau Lauik Flyover in Accordance with PDGJ 2021

Abstract

The construction of the Sitinjau Lauik Flyover represents a strategic solution to address accident-prone segments in an area characterized by extreme topography. However, its safety performance must be validated at the planning stage. This study aims to evaluate the geometric safety of the proposed flyover in accordance with the latest Indonesian Highway Geometric Design Guideline (PDGJ 2021) using an ex-ante approach. In addition, the study seeks to identify critical segments with limited safety margins that may require additional safety treatments before operation. The evaluated parameters include horizontal alignment, vertical alignment, and stopping sight distance (SSD) at a design speed of 40 km/h. The quantitative analysis indicates that all geometric parameters comply with the minimum requirements of PDGJ 2021, with curve radii ranging from 97 m to 2800 m (R_min = 57 m), superelevation values between 2.10% and 5.20%, SSD between 43 m and 54 m, and vertical grades from −1.00% to 13.00%. Although the design satisfies the prescribed standards, critical safety margins were identified at segments with radii ≤110 m and grades ≥12%, where SSD values approach the minimum threshold. The novelty of this study lies in the early-stage risk identification during the design phase in mountainous terrain. It is concluded that ex-ante evaluation is essential for determining the need for additional safety measures at locations with limited safety margins to mitigate accident risks before operation.

Keywords: Geometric safety; ex-ante evaluation; PDGJ 2021; Sitinjau Lauik Flyover; safety margin