Operational Reliability of Hard Shoulder Running on Freeways

Hard shoulder running is an effective measure to increase the capacity of freeways during peak hours. In most applications, particularly in Europe, opening and closing the hard shoulder for travel is dynamically controlled depending on the prevailing traffic conditions. By using the hard shoulder as an additional travel lane, the mean capacity of a freeway carriageway is significantly increased, resulting in less congestion and shorter travel times. However, operational reliability might be affected by incidents during which the hard shoulder is blocked and therefore not available for travel, leading to higher variance in the capacity distribution. In this study, the operational reliability of freeway segments with dynamic hard shoulder running in Germany was analyzed based on operating protocols and detector data. By comparing the capacity distributions estimated with and without traffic breakdowns following a closure of the hard shoulder during peak hours, it was found that incidents blocking the hard shoulder, although occurring quite often, had only a minor impact on capacity variability.