Size and sign of time savings

INTRODUCTION The conventional approach in the U.K. has been to value all travel time changes at a constant rate regardless of their size or direction. This ‘constant unit value’ approach was supported by the 1980-86 UK DoT Value of Time Study (MVA/ITS/TSU, 1987). However, there has always remained a vocal body of opinion critical of this approach (see Welch and Williams, 1997, for references and discussion). Some of the main objections have been the following: i. small amounts of time are less useful than large amounts; ii. small time savings (or losses) might not be noticed by travellers and any that are not noticed cannot be valued by those affected and so should not be valued by society; iii. small time savings are said to often account for a large proportion of scheme benefits, so that small errors in measurement might mean that the scheme is really of no benefit to anyone; iv. allowing small time savings to have ‘full’ value is said to inflate the measured total of benefits and so lead to schemes (often road schemes) being wrongly found to have sufficient net benefit to justify implementation; v. time savings are less highly valued than are time losses, according to surveys, and so should have a lower unit value when evaluating schemes. Both aspects relate to the possible non-constancy of the value of time for a given journey made for a given purpose (clearly, it is much less controversial, and indeed standard practice, to allow for variation by purpose and traveller type). The practical difficulties are twofold. On the one hand, it is difficult to overcome the lay reaction that small time savings have little or no value, as well as the feeling that losses are more important than gains. On the other hand, if these points have any empirical relevance, they cause major problems for the cost-benefit calculus, as losses and gains will not cancel out, and time savings cannot be directly aggregated. Although they do not recommend that values differentiated by size and sign should be used for appraisal, the HCG/Accent (1999) Report (AHCG) notes that [p 259] "For any level of variation around the original journey time, gains (savings) are valued less than losses. For non-work related journeys, a time savings of five minutes has negligible value." A recent paper by Gunn (2001) notes that corroborative results are available from a reanalysis of the 1988 Dutch value of Time study. For reasons which will be carefully rehearsed in this paper, we do not believe that the conclusion on the differences between gains and losses is safe. This is based on an extensive re-analysis of the AHCG data. We have found it harder to reach a conclusion on the issue of small time savings, we agree with AHCG that their data undoubtedly implies a lower valuation: we have some concerns, nonetheless, as to the interpretation which should be placed on this

Size and sign of time savings

INTRODUCTION The conventional approach in the U.K. has been to value all travel time changes at a constant rate regardless of their size or direction. This ‘constant unit value’ approach was supported by the 1980-86 UK DoT Value of Time Study (MVA/ITS/TSU, 1987). However, there has always remained a vocal body of opinion critical of this approach (see Welch and Williams, 1997, for references and discussion). Some of the main objections have been the following: i. small amounts of time are less useful than large amounts; ii. small time savings (or losses) might not be noticed by travellers and any that are not noticed cannot be valued by those affected and so should not be valued by society; iii. small time savings are said to often account for a large proportion of scheme benefits, so that small errors in measurement might mean that the scheme is really of no benefit to anyone; iv. allowing small time savings to have ‘full’ value is said to inflate the measured total of benefits and so lead to schemes (often road schemes) being wrongly found to have sufficient net benefit to justify implementation; v. time savings are less highly valued than are time losses, according to surveys, and so should have a lower unit value when evaluating schemes. Both aspects relate to the possible non-constancy of the value of time for a given journey made for a given purpose (clearly, it is much less controversial, and indeed standard practice, to allow for variation by purpose and traveller type). The practical difficulties are twofold. On the one hand, it is difficult to overcome the lay reaction that small time savings have little or no value, as well as the feeling that losses are more important than gains. On the other hand, if these points have any empirical relevance, they cause major problems for the cost-benefit calculus, as losses and gains will not cancel out, and time savings cannot be directly aggregated. Although they do not recommend that values differentiated by size and sign should be used for appraisal, the HCG/Accent (1999) Report (AHCG) notes that [p 259] "For any level of variation around the original journey time, gains (savings) are valued less than losses. For non-work related journeys, a time savings of five minutes has negligible value." A recent paper by Gunn (2001) notes that corroborative results are available from a reanalysis of the 1988 Dutch value of Time study. For reasons which will be carefully rehearsed in this paper, we do not believe that the conclusion on the differences between gains and losses is safe. This is based on an extensive re-analysis of the AHCG data. We have found it harder to reach a conclusion on the issue of small time savings, we agree with AHCG that their data undoubtedly implies a lower valuation: we have some concerns, nonetheless, as to the interpretation which should be placed on this

Market segmentation analysis

INTRODUCTION This working paper presents the findings of research aimed at assessing differences in the value of time by market segment. It draws on findings presented in AHCG’s final report to DETR (AHCG, 1996) and previous research conducted during the course of this research contract (Bates and Whelan, 2001) and it is intended that this document be read in conjunction with those two reports. The paper describes the estimation of a base model for each journey-purpose (business, commuting and other) and shows how each is influenced by: income, journey distance, cost reimbursement, congestion, vehicle occupancy, trip sub-purpose, occupation, age group, gender, household type, ‘free time’, respondent type, time constraints and geographical region. The findings of this analysis are then drawn together to develop a final set of models that allow the value of time to vary across a range of market segments. All models are estimated using GAUSS (Aptech Systems) without taking account of the repeat observations nature of the stated preference data

Relativistic scalar fields and the quasi-static approximation in theories of modified gravity

Relativistic scalar fields are ubiquitous in modified theories of gravity. An important tool in understanding their impact on structure formation, especially in the context of N-body simulations, is the quasi-static approximation in which the time evolution of perturbations in the scalar fields is discarded. We show that this approximation must be used with some care by studying linearly perturbed scalar field cosmologies and quantifying the errors that arise from taking the quasi-static limit. We focus on f(R) and chameleon models and link the accuracy of the quasi-static approximation to the fast/slow-roll behaviour of the background and its proximity to {\Lambda}CDM. Investigating a large range of scales, from super- to sub-horizon, we find that slow-rolling ({\Lambda}CDM-like) backgrounds generically result in good quasi-static behaviour, even on (super-)horizon scales. We also discuss how the approximation might affect studying the non-linear growth of structure in numerical N-body simulations.Comment: 19 pages, 9 figure

The Role of Intellectual Virtues in the Development of the Science Teacher: An Initial Provocation

Initial, informal observations of work with pre-service chemistry and other science teachers suggest that a number of intellectual virtues are required, alongside a shift in identity, in order to help secondary school science students negotiate the pathway from ‘science learner’ to ‘scientist’. This article explores these virtues, the ontological shift that accompanies them and pedagogical suggestions for how these attributes might be promoted in a programme of pre-service training, along with suggestions for further empirical research which might form the basis of further investigation into these initial observations

Lost Decades: Lessons from Post-Independence Latin America for Today's Africa

Africa and Latin America secured their independence from European colonial rule a century and half apart: most of Latin America after 1820 and most of Africa after 1960. Despite the distance in time and space, they share important similarities. In each case independence was followed by political instability, violent conflict and economic stagnation lasting for about a half-century (lost decades). The parallels suggest that Africa might be exiting from a period of post-imperial collapse and entering a period of relative political stability and economic growth, as did Latin America a century and a half earlier.

Income and distance elasticities of values of travel time savings: New Swiss results

This paper presents the findings of a study looking into the valuation of travel time savings (VTTS) in Switzerland, across modes as well as across purpose groups. The study makes several departures from the usual practice in VTTS studies, with the main one being a direct representation of the income and distance elasticity of the VTTS measures. Here, important gains in model performance and significantly different results are obtained through this approach. Additionally, the analysis shows that the estimation of robust coefficients for congested car travel time is hampered by the low share of congested time in the overall travel time, and the use of an additional rate-of-congestion coefficient, in addition to a generic car travel time coefficient, is preferable. Finally, the analysis demonstrates that the population mean of the indicators calculated is quite different from the sample means and presents methods to calculate those, along with the associated variances. These variances are of great interest as they allow the generation of confidence intervals, which can be extremely useful in cost-benefit analyses

Modelling of signal uncertainty and control objectives in robust controller design

This work develops a new paradigm for optimal robust controller synthesis in the frequency domain. A detailed examination is made of the engineering motivation and engineering efficacy underlying the various strands of robust control theory. The modelling of (a) signal uncertainty and (b) control system objectives in both Tioo and C\ control theories is considered in particular detail. Based on this examination, a theory which can fa irly be described as ‘a m odified 7ioo control theory’ or ‘a frequency domain C\ control theory’ is proposed. New signal sets for the modelling of uncertain signals are introduced. It is argued that these models more faithfully capture the way in which uncertain signals act on real physical systems. It is shown that by adopting these new models for uncertain signals, control theory can be used to non-conservatively minimise maximum tracking errors in the time domain, in the SISO case. In the MIMO case, the problem of optimally synthesising a controller to non-conservatively minimise tracking errors in the time domain leads to a modest variation on existing control theory, requiring the usual norm to be modified slightly. It is argued th a t the proposed paradigm in general achieves a better quality of control and more fa ith fu lly expresses the true objectives of feedback control systems. The proposed development is seen to also extend naturally to Ti.2 control theory, and indeed provides a new deterministic justification for the 7^2 control problem in the MIMO case. The question of design transparency in the synthesis of optimal robust controllers for multivariable systems is considered in detail. The implications of the proposed paradigm for transparency of design and weighting function selection are detailed. A decoupling design procedure for robust controller synthesis is proposed which, under certain restrictive conditions, allows the calculation of super-optimal robust controllers on a loop by loop basis. The usefulness of a classical decoupling approach to MIMO control system design in the context of multivariable robust control theory is demonstrated. A number of design examples are presented which show how the ideas and methods developed in this work can be applied to realistic control problems