The results of the analysis of the operation of heavy-duty vehicles with high load capacity (tractor units with trailers) have been presented. The road transport of cargo relies heavily on vehicles of this type. Performing this role is associated with high energy consumption. Laden and unladen driving were investigated. The collected data guaranteed the constancy of numerous parameters, including the investigation of the same model vehicles under both loaded and unloaded conditions on identical roads. The assessment focused on changes in driving techniques and energy consumption during significant variations in vehicle weight. The evaluation was grounded in the measurement results of kinematic parameters, namely driving speed, acceleration, and braking deceleration. The aforementioned parameters are typically employed in analysing driving techniques (DBP—driver behaviour profile). The energy consumption of traffic was then assessed in light of the analysed changes in driving technique. The weight of the load was 24 t, increasing the weight of the vehicle by 175%. The increase in weight has caused a 68.4% increase in the energy required for driving. The change in vehicle mass has a relatively minor effect on the average, median, and modal values of driving speed. In contrast, the impact on acceleration is far greater. This is partly because the examined models of tractor units are equipped with high-power engines (420 hp). Furthermore, 81% of the roads used for transportation tasks are motorways and expressways.