  We investigate a model for driven exclusion processes where internal states
are assigned to the particles. The latter account for diverse situations,
ranging from spin states in spintronics to parallel lanes in intracellular or
vehicular traffic. Introducing a coupling between the internal states by
allowing particles to switch from one to another induces an intriguing
polarization phenomenon. In a mesoscopic scaling, a rich stationary regime for
the density profiles is discovered, with localized domain walls in the density
profile of one of the internal states being feasible. We derive the shape of
the density profiles as well as resulting phase diagrams analytically by a
mean-field approximation and a continuum limit. Continuous as well as
discontinuous lines of phase transition emerge, their intersections induce
multicritical behavior.
