Entrainment and unit velocity: Surprises in an accelerated exclusion   process
  We introduce a class of distance-dependent interactions in an accelerated exclusion process (AEP) inspired by the observation of transcribing RNA polymerase speeding up when "pushed" by a trailing one. On a ring, the AEP steady state displays a discontinuous transition, from being homogeneous (with augmented currents) to phase-segregated. In the latter state, the holes appear loosely bound and move together, much like a train. Surprisingly, the current-density relation is simply $J=1-\rho$, signifying that the "hole-train" travels with \textit{unit} velocity. 
Jiajia Dong, Stefan Klumpp, Royce K.P. Zia
cond-mat.stat-mech