Estimating vehicular emissions on a main arterial road in Arar, Saudi Arabia: Insights for sustainable urban mobility

Rapid motorization in Saudi Arabia's secondary cities is intensifying concerns about local air quality, yet empirical, corridor-scale emission data remain scarce.This study integrates high-resolution traffic counts with regionally calibrated emission factors to characterize on-road pollutant loads along two arterial segments in Arar: (i) a freeflow highway section (Point A) and (ii) an urban, signal-controlled intersection (Point B).Vehicle volumes and classifications were recorded at 1-h resolution over seven consecutive days using MetroCount pneumatic sensors, capturing 53,749 and 55,116 vehicles at Points A and B, respectively.Baseline emission factors were derived from COPERT-6 and MOVES-5 models; to reflect local fleet age, fuel sulphury content and ambient temperatures, factors were uplifted by +15% for light-duty vehicles and +10-12% for heavy-duty vehicles.Despite similar traffic volumes, congestion at Point B markedly elevated pollutant intensities.Average weekday peak-hour speeds fell to 44.1 km/h for passenger cars and 29.9 km/h for heavy trucks, compared with 53.4 km/h and 42.7 km/h at Point A. Consequently, Point B exhibited 75% higher heavy-truck CO₂ emissions (1.27 × 10⁶ g/day/km) and increases of 75% and 74% in NOₓ (1 245 g/day/km) and PM₂.₅ (16.4 g/day/km), respectively, relative to Point A. Although heavy-duty vehicles comprised less than 7% of the fleet, they accounted for ≈ 50% of corridor-wide NOₓ and PM₂.₅.A review of mitigation strategies suggests that restoring average speeds above 50 km/h or rerouting Euro VI-compliant trucks could reduce corridor PM₂.₅ by ~20%.The findings reveal the main determinants of urban emission hotspots along the two principal arterial roads of mid-sized cities such as Arar.The insights from this study can support decision-makers in formulating medium-and long-term urban mitigation strategies to address the increasing roadside exposure in rapidly urbanizing Middle Eastern cities.