  We introduce driven exclusion processes with internal states that serve as
generic transport models in various contexts, ranging from molecular or
vehicular traffic on parallel lanes to spintronics. The ensuing non-equilibrium
steady states are controllable by boundary as well as bulk rates. A striking
polarization phenomenon accompanied by domain wall motion and delocalization is
discovered within a mesoscopic scaling. We quantify this observation within an
analytic description providing exact phase diagrams. Our results are confirmed
by stochastic simulations.
