Stationary states in two-lane traffic: Insights from kinetic theory.

Kinetics of dilute heterogeneous traffic on a two-lane road is formulated in the framework of Ben-Naim-Krapivsky model and stationary state properties are analytically derived in the asymptotic limit. The heterogeneity is introduced into the model as a quenched disorder in desired speeds of vehicles. The two-lane model assumes that each vehicle or platoon in a lane moves ballistically until it approaches a slow-moving vehicle or platoon and then joins it. Vehicles in a platoon are assumed to escape the platoon at a constant rate by changing lanes after which they continue to move at their desired speeds. Each lane is assumed to have a different escape rate. As the stationary state is approached, the platoon densities in the two lanes become equal, whereas the vehicle densities and fluxes are higher in the lane with lower escape rate. A majority of the vehicles enjoy a free flow if the harmonic mean of the escape rates of the lanes is comparable to average initial flux on the road. The average platoon size is close to unity in the free-flow regime. If the harmonic mean is lower than the average initial flux, then vehicles with desired speeds lower than a characteristic speed v^{} still enjoy free flow while those vehicles with desired speeds that are greater than v^{} experience congestion and form platoons behind the slower vehicles. The characteristic speed depends on the mean of escape times [R=(R_{1}+R_{-1})/2] of the two lanes (represented by 1 and -1) as v^{}∼R^{-1/μ+2}, where μ is the exponent of the quenched disorder distribution for desired speed in the small speed limit. The average platoon size in a lane, when v^{}≪1, is proportional to R^{μ+1/μ+2} plus a lane-dependent correction. Equations for the kinetics of platoon size distribution for two-lane traffic are also studied. It is shown that a stationary state with platoons as large as road length can occur only if the mean escape rate is independent of platoon size.