  The single-particle contributions to the optical conductivity of the
quasi-one-dimensional systems has been reexamined by using the gauge-invariant
transverse microscopic approach. The valence electrons are described by a model
with the weak bond-energy dimerization, while the relaxation processes are
taken into account phenomenologically. It turns out that the interband
conductivity of the insulating half-filled case fits well the single-particle
optical conductivity measured in various CDW systems. In the metallic regime,
for the doubled Fermi vector 2k_F close to \pi/a, the conduction electrons
exhibit a non-Drude low-frequency response, with the total spectral weight
shared between the intraband and interband channels nearly in equal
proportions. For 2k_F - \pi/a not to small, the behaviour of the conduction
electrons can be described as the response of a simple Drude metal.
