Line Length versus Operational Reliability

Abstract

The unreliability of public transportation is a well-known problem. During the design stages of public transportation, little attention is paid to operational reliability, although many design choices have a great impact on schedule adherence. During network design, operational reliability should be taken into account as a design parameter. This paper deals with line length. A new design dilemma is introduced: the length of the line versus operational reliability. Long lines offer many direct connections, thereby lowering the need for transfers. However, the variability is often negatively related to the length of a line and leads to less adherence to the schedule and additional waiting time for passengers. This paper suggests that both the positive and the negative effects of extending or connecting a line be taken into account. A tool that can be used to calculate the additional waiting time because of variability and transfers and that is based on actual journey and passenger data was developed. A case study in The Hague, Netherlands, shows that in the case of long lines with large variability, splitting of the line could result in less additional travel time because of improved operational reliability. This benefit compensates for the additional transfer time, provided that the transfer point is well chosen. This research shows the effect of choosing the transfer point at stops with many and fewer passing travelers. The latter could lead to a decrease in additional waiting time of about 30%. The splitting of a long line into two lines with an overlap in the central part could result in even more time savings. In that case, fewer travelers must transfer.