Efficiency versus fairness in network-wide ramp metering

Review of road traffic control strategies

“…Some recent studies have demonstrated that efficient ramp metering strategies (employing optimal control algorithms) may provide spectacular improvements (50% reduction of total time spent) in large-scale freeway networks [56], [58]. This may also be demonstrated via suitable treatment of real (congested) freeway traffic data; see [59].…”

“…The nonlinear traffic dynamics may be expressed by use of suitable macroscopic dynamic models in the state-space form [56], [57] ( 27) where the state vector comprises all traffic densities and mean speeds of 500-m-long freeway sections, as well as all ramp queues; the control vector comprises all controllable ramp volumes; the disturbance vector comprises all on-ramp demands and turning rates at bifurcations (including off-ramps). Generally, the evolution of traffic density is described via the conservation-of-vehicles equation, while the mean speed is calculated via an empirical (static or dynamic) equation in dependence of the traffic density.…”

“…This problem or variations thereof was considered and solved in various works [56], [67], [89]- [96]. Although simulation studies indicate substantial savings of travel time and substantial increase of throughput [56], advanced control strategies of this kind have not been implemented in the field as of yet.…”

Review of road traffic control strategies

“…• consider equity aspects for users of different ramps in the network [56], [85]. Such a comprehensive dynamic optimal control problem may be formulated and solved with moderate computation time by use of suitable numerical algorithms.…”

“…Although simulation studies indicate substantial savings of travel time and substantial increase of throughput [56], advanced control strategies of this kind have not been implemented in the field as of yet. Fig.…”