| 1. |
- Abate, Megersa, 1980-, et al.
(författare)
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A disaggregate stochastic freight transport model for Sweden
- 2018
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Ingår i: Transportation. - : Springer New York LLC. - 0049-4488 .- 1572-9435. ; , s. 1-26
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents estimation results for models of transport chain and shipment size choice, as well as an implementation of the estimated disaggregate models (for two commodity groups), in the context of the national freight transport model for Sweden. The new model is a disaggregate and stochastic (logit) model, whereas the existing Swedish national model is deterministic. One advantage of the new approach is that it bases the underlying behavior of shippers on a stronger empirical foundation (that is micro-data from the Swedish Commodity Flow Survey, CFS). Another advantage is that it overcomes a well-known disadvantage of deterministic models that lead to implausibly large responses to changes in scenario or policy variables. Although estimation and implementation of aggregate stochastic models were done before, in the context of a national freight transport forecasting model, we think this is the first implementation of disaggregate freight transport chain and shipment size models estimated on choice data for individual shipments, certainly in Europe. We carried out a number of model runs with both versions of the implemented model to compare elasticities and found that transport cost and time elasticities for tonne-km are smaller (in absolute values) in the disaggregate stochastic model than in their deterministic counterparts.
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| 2. |
- Abate, Megersa
(författare)
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Determinants of Capacity Utilisation in Road Freight Transportation
- 2014
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Ingår i: Journal of Transport Economics and Policy. - 0022-5258 .- 1754-5951. ; 48, s. 137-152
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Tidskriftsartikel (refereegranskat)abstract
- Recent performance indicators in the European road freight transport sector show there is an excess capacity. To shed light on this, this paper studies two aspects of capacity utilisation in trucking: the extent of empty running and the load factor. Using a joint econometric modelling framework, the paper shows that they can be explained as a function of haul, carrier, and truck characteristics. For estimation, a unique dataset from the Danish heavy vehicle trip diary was used. The results indicate distance and being a for-hire carrier have a positive effect on capacity utilisation, whereas the effect of truck size is non-linear.
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| 3. |
- Abate, Megersa
(författare)
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Economic effects of air transport market liberalization in Africa
- 2016
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Ingår i: Transportation Research Part A. - : Elsevier. - 0965-8564 .- 1879-2375. ; 92, s. 326-337
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Tidskriftsartikel (refereegranskat)abstract
- Although the aviation industry is increasingly becoming important for Africa's economic development and integration, the ability of airlines to access foreign markets remains hindered by restrictive regulatory policies. Attempts have been made to fully liberalize the intra-African air transport market. Except for general assertions about the merits/demerits of liberalization, our empirical understanding of the welfare effects of such polices in Africa remains rudimentary. This study empirically measures the economic effects of air transport liberalization, mainly on two supply side variables: fare and service quality, measured as departure frequency. The empirical models evaluate how air fares and departure frequency respond to measures of openness in air services agreements, while controlling for other determinants. The results show up to 40% increase in departure frequency in routes that experienced some type of liberalization compared to those governed by restrictive bilateral air service agreements. Furthermore, there is a relatively larger increase in departure frequency in routes which experienced partial liberalization compared to fully liberalized ones. This can be explained by the diminishing marginal effect of progressive liberalization on departure frequency. While the effect of liberalization is substantial in improving service quality, there is no evidence of its fare reducing effect.
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| 4. |
- Abate, Megersa, et al.
(författare)
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The optimal shipment size and truck size choice : The allocation of trucks across hauls
- 2014
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Ingår i: Transportation Research Part A. - : Elsevier BV. - 0965-8564 .- 1879-2375. ; 59, s. 262-277
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Tidskriftsartikel (refereegranskat)abstract
- There has been a growing interest in understanding how firms allocate their trucks across hauls, and how this allocation changes under various economic environments. This study investigates how variations in route/haul, carrier and vehicle characteristics affect the optimal vehicle size choice and the associated choice of shipment size. We show that the two choices are derived from the same optimization problem. There can be a continuum of shipment sizes, but decision-makers in freight transport have to choose from a limited number of vehicle alternatives. Therefore, we use a discrete-continuous econometric model where shipment size is modeled as a continuous variable, and vehicle size/type choice as a discrete variable. The results indicate that when faced with higher demand, and during longer trips firms are more likely to use heavier vehicles and ship in larger quantities which suggest that firms are realizing economies of scale and economies of distance. The study also discusses the effect of vehicle operating cost on the vehicle selection process and its policy implications.
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| 5. |
- Abdallah, Clement Kamil, et al.
(författare)
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Assessing the quality of water used for vegetable irrigation in Tamale Metropolis, Ghana
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- This paper assesses water quality that is used for vegetable irrigation in Tamale Metropolis, Ghana. A mixed-method of research design was employed in this study to collect and analyze the data based on survey instruments. The paper found that Escherichia coli (E. coli) that is usually used as an indicator of water contamination and heavy metals exist in all taken water samples. The mean concentrations of nutrients such as ammonia, nitrate, nitrite and phosphate were recorded as 0.022 mg/l to 5.98 mg/l for ammonia, 1.06 mg/l to 7.52 mg/l for nitrate, 0.031 mg/l to 0.056 mg/l for nitrate and 0.037 mg/l to 0.069 mg/l for phosphate. E. coli and Total Coliforms levels for Sanghani, Kamina and Waterworks from the laboratory analysis were recorded as 3.2x10(3) CFU 100 m/l and 5.5x10(2) CFU 100 m/l, 4.0x10(3) CFU 100 m/l and 1x10(2) CFU 100 m/l, and 2.1x10(3) CFU 100 m/l and 4.6x10(2) CFU 100 m/l respectively. To conclude, based on the measured parameters, water used for irrigation in the Tamale Metropolitan is polluted and may cause potential health risks. Therefore, farmers, traders and consumers need to apply further safety measures to make the vegetables safe.
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| 6. |
- Abed, Ahmed, et al.
(författare)
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Uncertainty analysis of life cycle assessment of asphalt surfacings
- 2024
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Ingår i: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 25:2, s. 219-238
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Tidskriftsartikel (refereegranskat)abstract
- The Life Cycle Assessment (LCA) of asphalt pavements are associated with significant uncertainty resulting from variability in the quantity and impact of individual components, the quality of data for each component, and variability of asphalt durability. This study presents a framework to quantify and incorporate the uncertainty of LCA and asphalt durability data into LCA of asphalt surfacings. The suggested framework includes: estimating the uncertainty of asphalt production processes by the pedigree matrix method, conducting a deterministic LCA, applying Monte Carlo Simulation (MCS) to estimate the probability density functions (PDFs) of the considered impacts using the uncertainty data, deterministic solution, and asphalt durability. This framework was applied to six asphalt mixtures; the results show that there is significant uncertainty in the processes that contribute to the environmental impacts. They also showed that considering asphalt durability and its uncertainty is critical and can significantly change the results and interpretation of LCA.
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| 7. |
- Abenoza, Roberto F., et al.
(författare)
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What is the role of weather, built-environment and accessibility geographical characteristics in influencing travelers’ experience?
- 2019
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Ingår i: Transportation Research Part A. - : Elsevier Ltd. - 0965-8564 .- 1879-2375. ; 122, s. 34-50
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Tidskriftsartikel (refereegranskat)abstract
- We examine the effect of weather, accessibility and built-environment characteristics on overall travel experience as well as the experience with the latest trips. These are factors that are often disregarded in the travel satisfaction literature even though they are believed to largely influence the first mile of the door-to-door trip. This study fills a research gap in investigating all these factors by using, amongst other, a relatively large travel satisfaction survey from years 2009 to 2015 and by focusing on urban and peri-urban geographical contexts, the city and county of Stockholm (Sweden), respectively. The ordered logit model results show that county dwellers living close to a metro station and in well linked-to-all areas report higher overall travel satisfaction evaluations. In addition, precipitation and ground covered with snow have a negative influence on travel satisfaction. Our findings indicate that built-environment characteristics exert a rather weak influence on the travel experience, especially in the peri-urban context. However, some aspects such as living in areas with medium densities, low income and with high safety perceptions around public transport stations are associated with higher satisfaction levels. In turn, areas with single land uses are found to have lower travel satisfactions. These results are important for public transport planners and designers in devising measures to prevent and mitigate the negative outcome of some weather conditions and to conceive better designed transit oriented developments.
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| 8. |
- Adolph, T., et al.
(författare)
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Development of compatibility assessments for full-width and offset frontal impact test procedures in FIMCAR
- 2014
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Ingår i: International Journal of Crashworthiness. - : Informa UK Limited. - 1358-8265 .- 1754-2111. ; 19:4, s. 414-430
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Tidskriftsartikel (refereegranskat)abstract
- The goal of the project FIMCAR (Frontal Impact and Compatibility Assessment Research) was to define an integrated set of test procedures and associated metrics to assess a vehicle's frontal impact protection, which includes self-And partner-protection. For the development of the set, two different full-width tests (full-width deformable barrier [FWDB] test, full-width rigid barrier test) and three different offset tests (offset deformable barrier [ODB] test, progressive deformable barrier [PDB] test, moveable deformable barrier with the PDB barrier face [MPDB] test) have been investigated. Different compatibility assessment procedures were analysed and metrics for assessing structural interaction (structural alignment, vertical and horizontal load spreading) as well as several promising metrics for the PDB/MPDB barrier were developed.The final assessment approach consists of a combination of the most suitable full-width and offset tests. For the full-width test (FWDB), a metric was developed to address structural alignment based on load cell wall information in the first 40 ms of the test. For the offset test (ODB), the existing ECE R94 was chosen. Within the paper, an overview of the final assessment approach for the frontal impact test procedures and their development is given.
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| 9. |
- Afridi, Muhammad Amjad, et al.
(författare)
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Municipal street maintenance challenges and management practices in Sweden
- 2023
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Ingår i: Frontiers in Built Environment. - : Frontiers Media S.A.. - 2297-3362. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The municipal street network acts as a multifunctional asset by providing people, vehicles and public services with a well-functioning infrastructure. To keep it in good condition, optimal maintenance measures are required which would result in an efficient use of taxpayers' money. This paper investigates the street network deterioration processes and the management practices that the municipal administrations have applied in Sweden. The study is based on a survey with Swedish municipalities using questionnaires and complementary interviews. The answers provide insight into a wide range of common pavement distresses and deterioration factors, along with pavement management practices. The study identifies that potholes, surface unevenness and alligator cracking are the most cited challenges, while pavement ageing, heavy traffic and patches are the most noted causes. Similarly, the cold climate and population density are influential factors in pavement deterioration. Allocation of the maintenance and rehabilitation and reconstruction budget is higher in the northern part of the country as well as in densely populated municipalities. Condition data collection and use of commercial Pavement Management Systems (PMS) are limited. Addressing the challenges effectively may be possible through the enhancement of the budget, feasible/clear guidelines from municipal councils/politicians, and reducing the gap between street network administrations and utility service providers.
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| 10. |
- Ahlberg, Joakim
(författare)
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Revenues in discrete multi-unit, common value auctions : a study of three sealed-bid mechanisms
- 2009
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Ingår i: Portuguese economic journal. - Lissabon : Springer. - 1617-9838. ; 8:1, s. 3-14
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Tidskriftsartikel (refereegranskat)abstract
- We propose in this paper a discrete bidding model, both on quantities and in pricing. It has a two-unit demand environment where subjects bid for contracts with an unknown redemption value, common to all bidders. Prior to bidding, the bidders receive private signals of information on the (common) value. Both the value and the signals are drawn from a known discrete affiliated joint distribution. The relevant task for the paper is to compare equilibrium strategies and the seller's revenue between the three auction formats. We find that, among the three auction formats below with two players, the Vickrey auction always gives the most revenue to the seller, where the discriminatory auction becomes second and the uniform auction last. We also find that, in equilibrium, bidders bid the same amount on both items in the discriminatory auction; a phenomenon we do not notice in either of the other two auction formats. There, different amount of demand reduction is encountered.
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