Ilka Dubernet


Last Name

Dubernet

First Name

Ilka

ORCID

0000-0003-4130-8303

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2017 - 20209
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Publications 1 - 9 of 9
  • The German value of time and value of reliability study
    Item type: Journal Article
    Dubernet, Ilka; Axhausen, Kay W. (2020)
    Transportation
    In 2012 Germany’s Federal Ministry of Transport and Digital Infrastructure (BMVI) initiated several projects in preparation of the new Federal Transport Infrastructure Plan (BVWP) 2030. This included an update of the general methodology and in particular of its cost–benefit analysis which is used to evaluate the effects of hundreds of German infrastructure projects under study. As part of the work the first official values of time (VOT) and values of reliability (VOR) for personal and business travel for Germany derived from a stated preference survey were estimated. From May 2012 until January 2013 nationwide data of more than 3000 participants was collected in a combined two-stage revealed and stated preference survey. This paper discusses the survey design, reports experience of the field phase and analyses the response behaviour of the sample. The stated choice experiments address mode, route, time of departure, workplace and residential location choice. The complex multi-attribute experiments of different types cover various aspects of short and long-term travel choice attributes which the respondent has to take into consideration during his decision process. Furthermore overlapping variables of the stated and revealed preference experiments enabled a joint estimation of the whole data for deriving the VOTs and VORs. Additionally numerous socio-demographic and attitudinal questions plus the large sample size for business and non-business trips make it a unique dataset offering various aspects of travel behaviour and their valuations to explore.
  • Comparing values of travel time obtained from residential, workplace and short-term decisions
    Item type: Working Paper
    Dubernet, Ilka; Dubernet, Thibaut Jean Pierre; Axhausen, Kay W. (2018)
    Arbeitsberichte Verkehrs- und Raumplanung
    The value of travel time (VTT) is an important element cost-benefit analysis of transportation projects, by encapsulating the willingness to pay of the population for improvements in the transport system. Those values are typically obtained from mobility behaviour data, in form of revealed or stated preference survey data. Although short-term decisions are typically used for this purpose, a growing number of authors is arguing that long-term decisions might provide more meaningful values for the evaluation of transportation projects, as those decisions have a longer-lasting effect on the experienced travel times. This paper uses data, which contains both, short- and long-term experiments, to investigate the impact of different time horizons on the valuation of time. In particular, two different long-term experiments (residential and workplace choice) in the dataset allow to evaluate not only the impact of the time horizon, but also the type of long-term decision. Using a joint model including all relevant choice situations, this paper investigates the difference in the valuation of time coming from different kind of choice experiments. The results show that the chosen time horizon does have a significant effect on the valuation of travel time and cost. Another finding is that the type of long-term decision and the structure of the choice experiment itself also influence the valuation. The resulting VTTs with a sharp decline by about a half for commute trips show an opposite effect to previous work. Thus this paper demonstrates the need for refinement of the definition of such a VTT.
  • Understanding the Value of Travel Time.
    Item type: Doctoral Thesis
    Dubernet, Ilka (2019)
    Project appraisal is an essential part of policy making, in transportation and elsewhere. To this end, different valuation methods are used. One of the most important evaluation tool is the Cost-Benefit-Analysis. Often, travel time savings account for the largest share of the gains in Cost-Benefit-Analyses. Therefore, they are a central element of the analyses, making its accurate determination of great importance for transport policy appraisal and investment decisions. The time changes are evaluated using the willingness to pay of travellers to save time resulting in the most important number in transport economics: the value of travel time. The \emph{German Value of Time and Value of Reliability Study} was the first official national study estimating values of travel time for Germany. For this purpose a large nationwide data set was collected. It covered six travel modes and five trip purposes, included several transport related attributes and different kinds of stated preference experiments, as well as two time horizons in the choice experiments. This great complexity and detail and the large sample size allows the investigation of various aspects and perspectives of time valuation. This thesis makes use of this rich data to compare a variety of approaches for travel time valuation, comparing different state-of-the-art model formulations, and covering more controversial topics, such as the use of values of time from long-term decisions. The values of time are derived using various model formulations and splits of the data. The impact of the method on the accuracy and trustworthiness of the estimates is evaluated, and used to make recommendations for future studies. The results show various interesting aspects. First, business as a travel purpose was found to be very special, and should thus ideally be modeled separately. Also shopping trips show different characteristics than the other purposes. Second, the VTT follows systematic patterns with changing agglomeration size, indicating that a differentiation on this level might be beneficial. Differentiating by local income, on the opposite, did not exhibit a recognisable pattern. Using a proven method to estimate the standard error of the estimated VTT, it was shown that for the formulation with the best model fit, a latent class model, accuracy in the VTT estimates was actually worse, illustrating how important error estimates are in the process of selecting the best model. A formulation of the VTT based on long term decisions did not bring any satisfying results. In particular, it seems that the other attributes that were part of the choice were valued much more strongly than changes in travel times. This thesis presents an in-depth and comprehensive evaluation of travel time with data from a national VTT study. The conclusions drawn from the analyses can be used as guidance for future transport project evaluation and policy making.
  • A dynamic approach to car availability throughout the life course
    Item type: Working Paper
    Crastes dit Sourd, Romain; Dubernet, Ilka; Beck, Matthew; et al. (2020)
    Arbeitsberichte Verkehrs- und Raumplanung
    The relatively new research field of mobility biographies designates the analysis of long-term mobility behaviour and the availability of mobility tools in a life span. A retrospective survey of the TU Dortmund, ETH Zurich and Goethe University Frankfurt collects data on individual mobility biographies of three different generations in a household with a life-calendar. Most of the past long-term decisions made by individuals such as buying a house or changing job affect their preferences in future periods and induce economic constraints in the form of transaction costs. Ignoring these aspects may lead to biased estimates in the analysis. A dynamic probit model is used to identify impacts on the individual decisions on car availability in a life span and tests for differences between gender or is used to include the time dependency of the explanatory variables such as age, the number of children or education. The focus of the paper is to compare the modelling results following common practices in the life course calendar literature, based on random effects probit models with the results obtained with a dynamic random effects probit model with autocorrelation. In contrary to the classic random effects probit model approach the main advantage of the dynamic probit approach is to explicitly model the correlated time-fixed and time-varying unobserved heterogeneity by the means of composite marginal likelihood estimation.
  • Context-dependent models (CRRM, MuRRM, PRRM, RAM) versus a context-free model (MNL) in transportation studies
    Item type: Journal Article
    Belgiawan, Prawira F.; Dubernet, Ilka; Schmid, Basil; et al. (2019)
    Transportmetrica A: Transport Science
  • Context-dependent models versus a context-free model
    Item type: Working Paper
    Belgiawan, Prawira F.; Dubernet, Ilka; Schmid, Basil; et al. (2017)
    Arbeitsberichte Verkehrs- und Raumplanung
    The random regret minimization (RRM) model considers the relative performance of the alternatives and is therefore context-dependent. In RRM, an individual, when choosing between alternatives, is assumed to minimize anticipated regret as opposed to maximize his/her utility. There are three variants of RRM, the classical CRRM, the μRRM, and the P-RRM. There is also a further approach called relative advantage maximization (RAM). We compare multinomial logit with the four mentioned alternatives. We use stated choice data sets which include mode choice, location choice, parking choice, carpooling, car-sharing. We compare the performance of those five models by their model fit, values of travel time savings (VTTS), and elasticities. Looking at the model fit, RAM outperforms the other models in five cases, whereas the PRRM does so in two cases and μRRM only for one case. The VTTS and elasticities vary substantially which is relevant for cost- benefit analysis or simplified modelling approaches.
  • Comparing values of travel time obtained from workplace and short-term decisions
    Item type: Working Paper
    Dubernet, Ilka; Dubernet, Thibaut Jean Pierre; Axhausen, Kay W. (2020)
  • The German value of time (VOT) and value of reliability (VOR) study
    Item type: Working Paper
    Dubernet, Ilka; Axhausen, Kay W. (2018)
    Arbeitsberichte Verkehrs- und Raumplanung
    In 2012 Germany’s Federal Ministry of Transport and Digital Infrastructure (BMVI) initiated several projects in preparation of the new Federal Transport Investment Plan (BVWP) 2030. This included an update of the general methodology and in particular of its cost-benefit analysis (CBA) which is used to evaluate the effects of hundreds of German infrastructure projects under study. As part of the work the first official values of time (VOT) and values of reliability (VOR) for personal and business travel for Germany were estimated. From May 2012 until January 2013 nationwide data of more than 3000 participants was collected in a combined two-stage revealed and stated preference survey. This paper discusses the survey design, reports experience of the field phase and analyses the response behaviour of the sample. The stated choice experiments address mode, route, time of departure, work place and residential/location choice. The complex multi-attribute experiments of different types cover various aspects of short and long-term travel choice attributes which the respondent has to take into consideration during his decision process. Furthermore overlapping variables of the stated and revealed preference experiments are suitable for a joint estimation of the whole data. Additionally numerous socio-demographic and attitudinal questions plus the large sample size for business and non-business trips make it a unique dataset offering various aspects of travel behaviour and its valuation to explore.
  • Comparing values of travel time obtained from workplace and short-term decisions
    Item type: Journal Article
    Dubernet, Ilka; Dubernet, Thibaut Jean Pierre; Axhausen, Kay W. (2020)
    Travel Behaviour and Society
    The value of travel time is an important element in cost-benefit analysis of transportation projects, by encapsulating the willingness to pay of the population for improvements in the transport system. Those values are typically obtained from mobility behavior data from revealed or stated preference surveys. Although short-term decisions are typically used for this purpose, a growing number of authors is arguing that long-term decisions might provide more meaningful values for the evaluation of transportation projects, as those decisions have a longer-lasting effect on the experienced travel times. This paper uses data which contains both short- and long-term experiments to investigate the impact of different time horizons on the valuation of time. Using a joint model including all short term, together with workplace choice situations, the differences in the valuation of time coming from different kinds of experiments are investigated. The results reveal difficulties to isolate the willingness to pay from other aspects of monetary compensation, such as income as a status or career progression symbol. The results confirm that the chosen time horizon has a significant effect on the valuation of travel time and cost. The richer data, compared to previous attempts at such an estimation, does reveal, however, potential pitfalls in the underlying theory, namely that there is a perfect substitution between travel costs and income. In particular, focusing on salary neutral situations instead of situations with salary gains changes the direction of the effect of long term decisions. Recommendations are derived for forthcoming studies.
Publications 1 - 9 of 9