Journal of Statistical Physics, Vol. 96, Nos. 12, 1999, p. 303-324.
We define a soft-spins approach to the driven lattice gas model (C-DLG) at the level of a master equation. As a result, we obtain a Langevin equation for the C-DLG which depends on the microscopic transition probabilities. We then show how this dependence affects the critical behavior of the the C-DLG, placing the finite- and the infinite-driving-field cases into different universality classes. In the same vein, we propose a continuum description of two other well-known anisotropic, conservative, nonequilibrium models: the two-temperature model (C-TT) and the randomly driven model (C-RDLG). We show that the C-RDLG with infinite averaged field and the C-TT with T_(II) = oo fall in the same universality class as the infinitely driven C-DLG. A Langevin equation for the driven bilayer lattice gas model is also presented.