Systems of equations of Vlasov-Fokker-Planck type are suggested for
multilane traffic flow. The equations include nonlocal and time-delayed
braking and acceleration terms with rates depending on the densities
and relative speeds. The braking terms include lane-change probabilities.
It is shown that simple natural assumptions on the structure of these
probabilities lead to multivalued fundamental diagrams, consistent with
traffic observations. Lane-changing behavior is the critical ingredient
in such bifunctions.