Line length vs. reliability: Network design dilemma in urban public transport

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

Read the full paper:Paper TRR 2009 Van Oort

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