## I. INTRODUCTION 

A driven lattice gas, or driven diffusive system, is a system of interacting particles that jump in a preferred direction on a lattice. The system cannot reach equilibrium but may attain a stationary state with a steady current; the model is a prototype for studies of nonequilibrium states [1–4]. The simplest example of a driven diffusive system, which has become one of the standard models of nonequilibrium statistical mechanics, is the totally asymmetric simple exclusion process (TASEP) [5–8]. In the TASEP with open boundaries the edge sites are connected to particle reservoirs with fixed densities. Introduced as a model of biopolymerization [9] and transport across membranes [10], over the years, this model has been applied to other processes, e.g., traffic flow [11], and cellular transport [12, 13]. 

From a mathematical point of view the model is of interest in the theory of in- teracting particle systems since, despite its simplicity, it shows a nontrivial behavior [7, 8, 14, 15]. In the one-dimensional TASEP with open boundaries, particles jump only to the right, along a one-dimensional lattice whose sites can be empty or occu- pied by a single particle. Particles are injected at the leftmost site at rate α if this site is empty, and removed at the rightmost site at rate β if this site is occupied. The one-dimensional TASEP, which has been solved exactly, exhibits three distinct phases in the α - β plane [16–19]. The phase transition is discontinuous along the line α = β < 1 / 2, where the density profile is linear, and continuous along the lines α = 1 / 2, α > β and β = 1 / 2, α < β (see Fig. 9). Although this model and and variants have been the subject of intensive theoretical study, there is as yet no realization of a TASEP-like system in the laboratory. 

The invention of optical tweezer arrays has permitted investigation of the dy- namics of colloidal particles in an external periodic potential [20–25]. The motion at long times and low friction consists of jumps between adjacent potential min- 

