<p>This paper investigates the effect of truck load exceeding the allowable load limit on asphalt pavement rutting performance and the resulting life cycle cost. Pavement materials were collected from a major expressway project in Oman and tested in the laboratory. Traffic data was obtained from the project design report. Dynamic modulus tests were performed to evaluate the asphalt layers’ moduli. Truck classification and axle weights were determined from field measurements. The study aimed to analyze the impact of load limit exceedance from the heaviest six-axle truck (T6) at different levels, while keeping the loads of other trucks at the allowable limit. Fifteen load cases exceeding the load limit (overweight) were examined, and the rutting damage was predicted using MEPDG models after calibration. Life cycle cost analysis (LCCA) was conducted to quantify the damage cost of truck overweight. The results indicated that the recorded GVW reached 116.7 t, representing 91.3% overweight. This resulted in an increase in rutting in the asphalt layers by 25% over 20 years. This corresponds to a reduction in service life by 43%. Life-Cycle Cost Analysis (LCCA) results indicated that exceeding the GVW limit for the six-axle truck by 91.3% results in an increase in maintenance cost by up to 90.8%. Pavement damage cost ranged from $0.008 to $0.093 per kilometer per lane for each six-axle truck, corresponding to GVW exceeding the allowable load limit by 6.6% to 91.3%, respectively.</p>