This study examines the effect of Low-Density Polyethylene (LDPE) modification on the brittleness and stiffness of bituminous concrete mixtures and develops a regression model to predict the brittleness ratio (SR). Experimental results reveal that adding LDPE significantly increases stiffness, with brittleness ratios ranging from 1.998 to 3.169. While higher stiffness improves resistance to permanent deformation and rutting, brittleness ratios above the critical limit of 3.0 indicate a risk of premature cracking, especially at low temperatures. This highlights the need to optimize LDPE content to balance stiffness and ductility. A regression model was created to predict brittleness based on proportions of granite (Z₁), sand (Z₂), bitumen (Z₃), and LDPE (Z₄). The model showed good statistical validity, with an F-calculated value of 1.382 (below the critical 2.48 at 5% significance) and an R² of 70.38%, explaining a significant portion of brittleness variability. The Mean Absolute Percentage Deviation of 7.2% between predicted and experimental values confirms its accuracy within acceptable engineering limits. These findings suggest that LDPE-modified bituminous concrete offers improved mechanical performance but requires careful LDPE dosage control to avoid excessive brittleness. The validated model serves as a practical tool for designing durable, sustainable asphalt pavements balancing stiffness and flexibility across diverse environments.