Simulation-based assessment of urban roadway expansion: Evaluating the new Bagamoyo Road Widening Project in Tanzania

During peak hours, many intersections in urban areas experience queuing, often leading to congestion. This study evaluated the operational impact of the New Bagamoyo Road Widening Project, a 4.3 km corridor in Dar es Salaam, Tanzania, spanning from the Morocco to Mwenge intersections. The project aimed to improve intersection performance and overall corridor efficiency by adding two lanes in each direction. A microscopic simulation using PTV VISSIM was conducted, supported by manually collected traffic count data from both before and after construction. The simulation model was calibrated using key driver behavior parameters, including look-ahead and look-back distances, temporary lack of attention, and desired speed distributions. Model accuracy was assessed using the GEH statistic and Root Mean Squared Normalized Error (RMSNE), with all junctions achieving GEH values below 5.0 and RMSNE values below 15 %, indicating a strong fit. Intersection performance was evaluated based on control delay and Level of Service (LOS) following the Highway Capacity Manual methodology. Before construction, all intersections operated at LOS F during peak hours. Post-construction results showed improvements, with several intersections reaching LOS C, B, and A, despite increased traffic volumes. While a paired t -test on the collective delay reduction was not statistically significant, a Cohen's d effect size of 0.44 indicated a small to moderate, practically meaningful operational improvement. These findings demonstrate that road widening, combined with access management, can effectively enhance urban mobility. The study supports the use of simulation-based evaluations in transport planning and offers insights for data-driven infrastructure decisions. It focuses on intersection operations and does not consider pedestrian safety, environmental impacts, or induced demand, areas recommended for future research.