  The 2D TI edge states are considered within the Volkov-Pankratov (VP)
Hamiltonian. A smooth transition between TI and OI is assumed. The edge states
are formed in the total gap of homogeneous 2D material. A pair of these states
are of linear dispersion, others have gapped Dirac spectra. The optical
selection rules are found. The optical transitions between the neighboring edge
states appear in the global 2D gap for the in-plane light electric field
directed across the edge.
  The electrons in linear edge states have no backscattering, that is
indicative of the fact of topological protection. However, when linear edge
states get to the energy domain of Dirac edge states, the backscattering
becomes permitted. The elastic backscattering rate is found. The Drude-like
conductivity is found when the Fermi level gets into the energy domain of the
coexistence of linear and Dirac edge states. The localization edge conductance
of a finite sample at zero temperature is determined.
