An Agenda for Research on Reliability
John Bates, John Bates Services, UK
The importance of reliability (more narrowly, travel time variability) as an attribute of transport level of service quality is well attested. However, translating this observation into models which can be used for scheme and policy appraisal remains a challenge. The aim of this paper is to reflect on what is currently known and what more is necessary to enable reliability to take its place as a standard component within transport modelling.
In a recent publication, Small & Verhoef (2007) state [p 55]:
The theory of time allocation is well developed and permits us to rigorously address con-
ceptual issues concerning value of time and reliability. Despite uncertainty, a consensus has developed over many of the most important empirical magnitudes for values of time, per-mitting them to be used confidently in benefit assessment. Another decade should bring similar consensus to value of reliability.?
Since two years have already elapsed, that gives us 8 years to reach the consensus! It will not be easy to make the authors? prediction come true.
In order to integrate reliability into our transport models, we need to know a) how changes in reliability will impact on demand, and b) how, for a given policy, the outturn reliability will be affected by the level of demand. Many studies have been carried out, and much has been learnt. Nevertheless, at the moment, we are some way off such a level of knowledge, but this applies particularly to the supply relationship.
The paper will deal with aspects of measurement, theory, and practical approximations, and, based on this, propose an agenda for research.
Ref: Small K A and Verhoef E T (2007), The Economics of Urban Transportation, Routledge, London & New York
Association for European Transport