Automated highway systems and hard-shoulders running: A case study

The purpose of this research was to evaluate the increase of capacity of existing motorway resulting from the implementation of relatively new traffic control strategies, as the automated highway systems (AHS) and the hard-shoulder running (HSR). Was examined the Italian motorway A22, belonging to Trans-European Road Network, corridor Helsinki - La Valletta. Many traffic surveys were done (year 2014) in several road sections. For each of them have been carried out the flow diagrams, the traffic flow parameters (capacity C, free flow speed vf,jam density kjam) and the relationship between flow rate of lane (right lane Qright and passing lane Qpass) and total flow rate Qt. The current carriageway capacities are in the range 2.703 veh/h ÷ 3.621 veh/h. To improve the capacity, a hard-shoulder running is planned, in both directions of the A22, for a total length of 128 km. This type of traffic control strategy allows an increase of the capacity up to 35%. Instead, for the hypothesized safety conditions of the platooned automated vehicles, a single lane with an AHS gives rise to a capacity of about 5.500 veh/h (reaction time δ= 0, 1 s).