  We study driven particle systems with excluded volume interactions on a
two-lane ladder with periodic boundaries, using Monte Carlo simulation, cluster
mean-field theory, and numerical solution of the master equation. Particles in
one lane are subject to a drive that forbids motion along one direction, while
in the other lane the motion is unbiased; particles may jump between lanes.
Despite the symmetry of the rates for transitions between lanes, the associated
particle densities are unequal: at low densities there is an excess of
particles in the undriven lane, while at higher densities the tendency is
reversed. Similar results are found for an off-lattice model. We quantify the
reduction in the stationary entropy caused by the drive. The stationary
two-point correlation functions are found to decay algebraically, both on- and
off-lattice. In the latter case the exponent governing the decay varies
continuously with the density.
