Measurement valuation of public transport reliability

Land Transport New Zealand has released a report that explores methods of measuring the value placed on public transport reliability in different contexts in New Zealand.

Reliability relates to an uncertainty in the time taken to travel from the start to the end of a person’s journey. For a public transport journey, reliability can affect users in one of two ways: as a delay when picking up the passenger and as a delay when the passenger is on the service. One or both of these sources of unreliability causes passengers to arrive at their destination at a different time than scheduled.

Reliability is important for operators and passengers alike. For operators, unreliable services cause difficulties in timetabling and resource planning. For passengers, unreliable services cause adjustments in an individual’s desired tripmaking behaviour to account for the possibility of a service not operating ‘as normal’. In particular, variable departure times force the traveller to arrive earlier at the service, and create uncertainty and anxiety about whether the service has arrived. Variable arrival times cause travellers to arrive at their destination late and force them to take an earlier service. In-vehicle time variability causes the traveller to experience uncertainty and anxiety about how long they will have to spend in the service.

Reliability measures are typically used within performance regimes to evaluate the quality of service of public transport providers. Most of these regimes are based on the percentage of services arriving on time.

Research carried out in 2007 outlined a method of measuring the value placed on public transport reliability in different contexts in New Zealand. As part of this research, a stated preference survey was designed and implemented to collect information about passengers’ current public transport usage, their attitudes to reliability and how they valued reliability.

Using these stated preference surveys, four initial models were estimated: a disaggregate model – valuing earliness and lateness; a mean model – using an ‘average minutes late’ variable; a variance model – using the standard deviation of reliability; and a mean-variance model – combining the average minutes late and standard deviation valuations. The preferred approach, based on ease of use and comparability to international measures, was the mean delay model.

A value of time was determined from the departure stated preference survey. Values of time ranged around $NZ8/hour. The surveys also found that rail users consistently had a value of time almost twice that of bus users, which is consistent with international findings.
Source: Vincent, M. 2008 Measurement valuation of public transport reliability. Land Transport New Zealand Research Report 339. 128 pp.

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