Road-geometry and traffic predictors of roadside soil contamination: Insights from PCA and LASSO modeling

Roadside environments are critical interfaces where transportation systems intersect with urban ecosystems, often acting as hotspots for the accumulation of potentially toxic elements (PTEs). In arid and semi-arid regions with aged vehicle fleets and fuel quality concerns, the persistence and dispersion of PTEs pose heightened environmental and public health risks. This study aimed to investigate the spatial patterns, potential sources, and environmental drivers of PTE concentrations (Pb, Cd, Zn, Cu, Ni, Cr) in roadside soils west of Isfahan City, Iran. Surface (0–2 cm) and background (30 cm) soils were collected from 209 stations, and analyzed using standard protocols with detection limits ranging from 0.1 to 1.0 ppm. Principal Component Analysis (PCA) identified two dominant components: PC1 (Zn, Cu, Cr) related to mechanical abrasion, and PC2 (Pb, Cd, Ni) linked to combustion sources. Least Absolute Shrinkage and Selection Operator (LASSO) regression and sensitivity analysis revealed that PC1 was primarily predicted by road slope and curvature, while PC2 was best explained by traffic volume and diesel vehicle proportion (R² = 0.561 and 0.686, respectively). The results highlight the dual role of structural and operational road factors in shaping PTE distribution in dryland cities, with implications for land-use planning and pollution mitigation in rapidly urbanizing regions.