Relaxation and retardation spectra are often used to describe the linear viscoelastic properties of polymer melts, asphalts, and other viscoelastic materials, since the spectra contain sufficient information from which other linear material functions can be easily calculated. The applicability of these functions strongly depends on the range of frequencies or relaxation times over which the experimental data were obtained. Various techniques can be employed to expand the range of relaxation times, which involves using different types of tests, such as oscillatory shear or creep. The overall range of relaxation times can be expanded by means of the time‐temperature superposition. In the case of bituminous materials studied, creep experiments at lower temperatures involve different testing geometry, e.g. a bending beam rheometer (BBR). The challenge is to combine the spectra obtained from the oscillatory and creep/recovery in shear deformation with the spectra obtained from the extended flexural deformation...