Re-evaluating speed management in Egypt: a microsimulation study on the safety and operational trade-offs of lane-based strategies

This study re-evaluates Egypt’s Differential Speed Limit (DSL) policy by proposing Lane-Based Speed Limits (LBSL), an innovative strategy where speed limits vary across highway lanes. To address a critical research gap, we developed a microsimulation framework using Simulation of Urban Mobility (SUMO) with parameters specifically justified for Egyptian driver behavior. While constrained by data availability, our model moves beyond generic defaults by integrating a key stand-still gap parameter (CC0 = 1.5 m) calibrated from previous research on Egyptian conditions, ensuring a more accurate representation of local driving patterns. We simulated three-lane highway scenarios under varying traffic volumes (500–1750 veh/h/lane), heavy vehicle percentages (2.5–20%), and speed limits (100, 110, 120 km/h). This compared LBSL configurations (speed reductions of 10, 15, and 20 km/h between lanes) against Uniform Speed Limit (USL) and current DSL strategies. Performance was assessed through average delay, travel speed, lane-changing frequency, and conflict ratios using Time-to-Collision thresholds (≤ 2.50, ≤ 1.50, and ≤ 0.50 s). The results indicate that Egypt’s existing DSL strategy offers no statistically significant safety advantages over USL, questioning its effectiveness. Conversely, LBSL significantly improved safety, reducing conflicts by up to 60%, though it introduced a trade-off with operational efficiency by increasing delays by 71–870%. The primary contribution is a contextually grounded analysis demonstrating LBSL as a safer strategic alternative to Egypt’s incumbent DSL policy. This provides Egyptian policymakers with evidence-based insights for potential traffic safety reforms and offers a methodological framework for adapting microsimulation to other regions with similar data constraints.