Abstract The paper presents the results of the bitumen studies, including the U.S. MSCR procedures describing bitumen creep under dynamic loading. It permits predicting the possibility of the damage in bituminous layers at high ambient temperatures and at low and high shear stresses. In addition, the study included such features as: the breaking point temperature, the complex modulus G*, the viscosity at low shear rates. The tests were performed generally for bitumen 35/50. The test results for asphalt 50/70 are only informative. Bitumen 35/50 (50/70) was modified with synthetic wax derived from the Fischer-Tropsch synthesis (F-T) in amounts of 1.5%, 2.5%, 3.0% and 4.0%. The assessment of the influence of the synthetic wax on basic properties of the bitumen has been enriched by means of quantitative analysis of the morphology of the modified bitumen by means of the fluorescence microscope. A summary of the entire analysis was performed using muliticriteria optimization which purpose was determining the optimal content (range) of the synthetic wax including its high stiffness and maintaining the satisfactory flexibility at a low temperatures.