On-road emissions from urban buses with SCR + Urea and EGR + DPF systems using diesel and biodiesel

Due to growing concerns about NO_x and particulate matter (PM) emissions from diesel engines, stricter regulations are being introduced requiring advanced emission control technology. In response the diesel industry has begun testing various emission control technologies and applying them. To assess vehicle renewal policies of bus companies, two exhaust after-treatment technologies are compared: the combination of a diesel particulate filter and an exhaust gas re-circulation system and the combination of a selective catalytic reduction and urea. On-board emission measurements were conducted under real-world driving conditions on a specific bus route in the city of Madrid.     

The influence of oceanographic scenarios on the population dynamics of demersal resources in the western Mediterranean: Hypothesis for hake and red shrimp off Balearic Islands

The aim of the present paper is to study the relationships between some climatic indices and parental stock, recruitment and accessibility to trawl fishery of hake (Merluccius merluccius) and red shrimp (Aristeus antennatus) off Balearic Islands (western Mediterranean). Available annual catch per unit effort, recruitment and spawning stock biomass have been used as biological data. As environmental data, the meso-scale IDEA index and the large-scale North Atlantic Oscillation (NAO) and Mediterranean Oscillation (MO) indices have been used. To analyze possible links between these indices with the population dynamics of demersal resources, two non-linear approaches have been applied: (i) stock–recruitment relationships from Ricker and Beverton–Holt models, by sequentially incorporating environment factors; (ii) generalized additive modelling, both classical general and threshold non-additive models were considered. The latter simulate an abrupt change in explicative variables across different phases (time periods or climatic index values). The results have shown that two oceanographic scenarios around the Balearic Islands, associated with macro and meso-scale climate regimes, can influence the population dynamics of hake and red shrimp. This is especially true for recruitment, which seems to be enhanced during low NAO and IDEA indices periods. During these periods, colder-than-normal winters generate high amounts of cold Western Mediterranean Intermediate Waters (WIW) in the Gulf of Lions, which flow southwards and reach the Balearic Islands channels in spring, increasing the productivity in the area. This oceanographic scenario could also be favourable to the distribution of hake on the fishing grounds where the trawl fleet targets this species, increasing its accessibility to the fishery. Both spawning stock and abundance of red shrimp seems to be also enhanced by high MO index periods, which could reflect the increased presence of the saline and warm Levantine Intermediate Waters (LIW) in the study area, extending over the fishing grounds of this species. The proposed interactions can be useful to assess and manage these important demersal resources.     

An optimization model for bus fleet replacement with budgetary and environmental constraints

ABSTRACT

As maintenance and operation costs increase with usage over time, equipment is replaced when the value of new equipment is more attractive. Some methods have been developed to solve this problem. In the public transport sector, such problems are frequently analyzed by fleet managers and determined by bus age restriction regulations. We propose an Integer Programming model that integrates both budgetary and environmental constraints (CO₂ emissions) which, as far as we know, have not previously been studied in conjunction. The study aims to determine the optimal replacement plan for a fleet of diesel buses of different size, age, maintenance costs and emissions rates, with new (less polluting) diesel buses over a time horizon of 50 years. The results indicate that it is possible to reduce emissions with a low annual budget using an optimal replacement policy.     

More gray hair—but for whom? Scenario-based simulations of elderly activity travel patterns in 2020

This paper reports the results of a scenario-based simulation study to explore mobility effects of an aging society in the Netherlands. Four accumulative behavioral scenario variants, embedded in an economic and demographic scenario are used to simulate possible future activity-travel patterns, using the Albatross system as the simulator. The variants account for likely differences in activity-travel behavior between elderly today and elderly in the future. Trends ongoing over the last decade in the Netherlands suggest that future elderly need to work longer, change their activity pattern with most growth occurring in the social/leisure activity category, will try to avoid morning peak hours by rescheduling their activities and may introduce more spatial diversity in terms of their residence location. Results show that these behavioral and spatial changes lead to a significant increase in travel demands as well as temporal, spatial and modal shifts in mobility patterns. We discuss possible policy implications of these predictions and evaluate the specific strength of activity-based models for studies of this kind.

Assessment of work-related risk criteria onboard a ship as an aid to designing its onboard environment

The environment onboard a ship presents a typical example of a severe environment, displaying extreme conditions of temperature and relative humidity, especially in the engine room. Datasheets, the international labour organization, and standards do not provide clear information about the suitable ambience of the engine room, its design conditions, and the role of marine engineers in preventing work-related risk. In this study, air temperature and relative humidity were monitored at several locations onboard a merchant ship. These real monitored data were then compared with the ISO design indications to obtain an effective work risk analysis. From these indoor temperature and relative humidity data, the corresponding parameters of thermal comfort in the engine control room and the heat stress and sweating index of a worker in the engine room were determined. As a function of these indices, the maximum time that a worker can stay in the engine room and the time for which he must rest in the control room were also calculated in the present study. Some design corrections are also proposed herein to improve these environments.     

Constrained nested logit model: formulation and estimation

A model of traveller behaviour should recognise the exogenous and endogenous factors that limit the choice set of users. These factors impose constraints on the decision maker, which constraints may be considered implicitly, as soft constraints imposing thresholds on the perception of changes in attribute values, or explicitly as hard constraints. The purpose of this paper is twofold: (1) To present a constrained nested logit-type choice model to cope with hard constraints. This model is derived from the entropy-maximizing framework. (2) To describe a general framework to deal with (dynamic) non-linear utilities. This approach is based on Reproducing Kernel Hilbert Spaces. The resulting model allows the dynamic aspect and the constraints on the choice process to be represented simultaneously. A novel estimation procedure is introduced in which the utilities are viewed as the parameters of the proposed model instead of attribute weights as in the classical linear models. A discussion on over-specification of the proposed model is presented. This model is applied to a synthetic test problem and to a railway service choice problem in which users choose a service depending on the timetable, ticket price, travel time and seat availability (which imposes capacity constraints). Results show (1) the relevance of incorporating constraints into the choice models, (2) that the constrained models appear to be a better fit than the counterpart unconstrained choice models; and (3) the viability of the approach, in a real case study of railway services on the Madrid–Seville corridor (Spain).     

The university workers’ willingness to pay for commuting

Using a dynamic approach, employing data on job mobility, we demonstrate that university workers?? marginal willingness to pay for reducing commuting distance is about ?0.25 per kilometre travelled. This corresponds to a marginal willingness to pay for reducing commuting time of about 75?% of the net average hourly wage. For females, the willingness to pay is substantially higher than for males. It is also substantially higher for workers that work few hours per day, as predicted by theory.     

The use of recovery time in timetables: rail passengers’ preferences and valuation relative to travel time and delays

Transportation - Recovery time in the rail industry is the additional time that is included in train timetables over and above the minimum journey time necessary often with the explicit aim of...     

Reassessing the commuting penalty for immigrants: new evidence from Spain

Transportation - This article examines the differences in commuting length between native and immigrant employees in Spain, a relevant issue since immigrants' longer commuting times may, among...     

Competition Between New Port Governance Models on the Iberian Peninsula

The aim of this article is to analyze the interaction between port devolution processes in Portugal and Spain in their common geographical environment, the Iberian Peninsula. Firstly a review is done of the different port devolution processes in the world which specifically analyses the transition of numerous public and centralized ports to the landlord model. Among the conclusions that we can highlight with respect to the Iberian port systems are the need for a reflection process before any change is made to the port governance model, and greater cooperation between the two countries to avoid any possible future port tariff price wars. The over-investment process that the Spanish port devolution process, especially, has generated must also be mentioned, for highlighting once again the almost inexhaustible ability of ports to eat up public funds for investment that precludes profitability.