Abstract

Civil aviation air traffic undergoes many random disturbances. Air traffic controllers watch the real traffic and ensure that it is free from collision hazards in the whole airspace — the ATC sector — under their control. The ATFM service takes care that the flow capacity in each sector, called capacity of the air traffic sector, is not exceeded. In the paper an original method of model estimation of the capacity of the designed ATC sectors is described. In this method an experimentally established statistical relationship between the random variables of control load and the air traffic density is used. The capacity of a sector was found from the joint probability distribution of such a two-dimensional random variable model determined as a quanti le of adequate order. This method was verified in practice by determining the capacity of the designed new ATC sectors in FIR Warsaw. Document type: Book

Abstract

This paper considers a congested bottleneck. A fast lane reserves a more than proportional share of capacity to a designated group of travellers. Travellers are otherwise identical and other travellers can use the reserved capacity when it would otherwise be idle. The paper shows that such a fast lane is always Pareto improving under Nash equilibrium in arrival times at the bottleneck and inelastic demand. It can replicate the arrival schedule and queueing outcomes of a toll that optimally charges a constant toll during part of the demand peak. Within some bounds, the fast lane scheme is still welfare improving when demand is elastic. Document type: Book

Abstract

Environmental impact assessment (EIA) is a systematic process designed to identify and predict the potential impacts of human activity on the biophysical and human environment. It also functions as an environmental management tool to identify measures to avoid, mitigate or compensate for those effects. EIA is intended to be an iterative process to follow-up to projects postimplementation to determine actual environmental outcomes, interpret and communicate information about those outcomes and investigate opportunities for improved project environmental performance. Originating from the United States’ National Environmental Policy Act of 1970, EIA is now amongst the most successful and widely practiced environmental management tools in the world. Key Concepts: EIA is an aid to decision making through which concerns about the potential environmental consequences of proposed projects are assessed before those projects become a reality. Screening in EIA ensures that assessments are done when needed and not done when not needed. Scope is essential to good EIA and the goal is to focus on a select set of environmental components that are deemed important from scientific, public or regulatory perspectives and are likely to be adversely affected by the project. The underlying intent of EIA is to allow project proponents, managers and decision makers to enhance the benefits of proposed development projects and to mitigate potentially adverse impacts to the point of acceptability. EIA must be applied early in the development planning processes if it is to be influential in project design and decision making. Information gained in EIA follow-up studies, after the project is implemented, provides feedback to improve predictions and mitigation and management programmes, and an opportunity to learn for subsequent project proposals. Keywords: environmental impact assessment; baseline studies; impact prediction; mitigation and management of impacts; cumulative environmental effects; follow-up studie

Abstract

The Time-Dependent Pollution-Routing Problem (TDPRP) consists of routing a fleet of vehicles in order to serve a set of customers and determining the speeds on each leg of the routes. The cost function includes emissions and driver costs, taking into account traffic congestion which, at peak periods, significantly restricts vehicle speeds and increases emissions. We describe an integer linear programming formulation of the TDPRP and provide illustrative examples to motivate the problem and give insights about the tradeoffs it involves. We also provide an analytical characterization of the optimal solutions for a single-arc version of the problem, identifying conditions under which it is optimal to wait idly at certain locations in order to avoid congestion and to reduce the cost of emissions. Building on these analytical results we describe a novel departure time and speed optimization algorithm for the cases when the route is fixed. Finally, using benchmark instances, we present results on the computational performance of the proposed formulation and on the speed optimization procedure.

Abstract

Most solution methods for the vehicle routing problem with time windows (VRPTW) develop routes from the earliest feasible departure time. However, in practice, temporal traffic congestions make that such solutions are not optimal with respect to minimizing the total duty time. Furthermore, VRPTW solutions do not account for complex driving hours regulations, which severely restrict the daily travel time available for a truck driver. To deal with these problems, we consider the vehicle departure time optimization (VDO) problem as a post-processing step of solving a VRPTW. We propose an ILP-formulation that minimizes the total duty time. The obtained solutions are feasible with respect to driving hours regulations and they account for temporal traffic congestions by modeling time-dependent travel times. For the latter, we assume a piecewise constant speed function. Computational experiments show that problem instances of realistic sizes can be solved to optimality within practical computation times. Furthermore, duty time reductions of 8 percent can be achieved. Finally, the results show that ignoring time-dependent travel times and driving hours regulations during the development of vehicle routes leads to many infeasible vehicle routes. Therefore, vehicle routing methods should account for these real-life restrictions.

Abstract

Daily traffic congestions form major problems for businesses such as logistical service providers and distribution firms. They cause late arrivals at customers and additional hiring costs for the truck drivers. The additional costs of traffic congestions can be reduced by taking into account and avoid well-predictable traffic congestions within off-line vehicle route plans. In the literature, various strategies are proposed to avoid traffic congestions, such as selecting alternative routes, changing the customer visit sequences, and changing the vehicle-customer assignments. We investigate the impact of these and other congestion avoidance strategies in off-line vehicle route plans on the performance of these plans in reality. For this purpose, we develop a set of VRP instances on real road networks, and a speed model that inhabits the main characteristics of peak hour congestion. The instances are solved for different levels of congestion avoidance using a modified Dijkstra algorithm and a restricted dynamic programming heuristic. Computational experiments show that 99% of late arrivals at customers can be eliminated if traffic congestions are accounted for off-line. On top of that, almost 70% of the extra duty times caused by the traffic congestions can be eliminated by clever avoidance strategies.

Abstract

In Europe, the preferential tax treatment of company cars implies that many employees receive a company car as part of their compensation package. In this paper, we consider a model in which wages and the decision whether or not to provide a company car are the result of direct negotiation between employer and employee. Using this framework, we theoretically and numerically study first- and second-best optimal tax policies on labour and transport markets, focusing on the role of the tax treatment of company cars. We obtain the following results. First, higher labour taxes and a more favourable tax treatment of company cars raise the fraction employees that receives a company car; congestion and congestion tolls reduce it. Second, in countries that provide large implicit subsidies to company cars, eliminating the preferential tax treatment of company cars may be an imperfect but quite effective substitute for currently unavailable congestion tolls. The numerical illustration, calibrated using Belgian data, suggests that it yields about half the welfare gain attainable through optimal congestion taxes. Third, the favourable tax treatment of company cars justifies large public transport subsidies; the numerical results are consistent with zero public transport fares. Finally, we find that earlier models that ignored the preferential tax treatment of company cars may have substantially underestimated optimal congestion tolls in Europe. The numerical illustration suggests that about one third of the optimal congestion toll we obtain can be attributed to the current tax treatment of company cars. (C) 2011 Elsevier Ltd. All rights reserved.

Abstract

The ownership form of Air Navigation Service Providers varies across countries, ranging from state agencies belonging to the Department of Transport, to government-owned corporations, to semi-private firms with for-profit or not-for-profit mandates. This research focusses on the link between the performance of ANSPs and their ownership form. Economic theory suggests that effort to achieve cost efficiency will be higher in the case of public companies with a board of stakeholders composed of airspace users and in the case of private companies with-stakeholders that are also shareholders. A stochastic frontier analysis estimation of the production and cost functions of 37 European air navigation service providers over nine years suggests that the public-private ownership form with stakeholder involvement achieves statistically significantly higher productive and cost efficient en-route levels compared to either a government corporation or a state agency. We also find substantial levels of inefficiency across the European air traffic control market.

Abstract

Because the payload that an airplane can carry is a function of the longest segment of its route and differs from route to route, the usual algorithms of network flow theory will not yield the optimum flow of payload. In this paper two network algorithms are described. They determine the route of maximum payload flow per hour of flight time and the maximum steady-state payload flow through a network with capacity constraints on the nodes.

Abstract

Over recent decades, research on antecedents of safety in High Reliability Organizations (HROs) has shifted from focusing mostly on technical issues to placing greater emphasis on human factors. Although an abundance of research suggests that human factors seem to play an important part in most accidents and near misses, there is still a shortage of research on the underlying mechanisms and processes involved in unsafe acts and safety critical behavior. Thus, many research questions regarding the impact of human factors still remain relatively unexplored. The fairly new direction of Positive Organizational Behavior (POB) has presented a fertile theoretical and methodological foundation for examining safety issues in HROs. One promising new POB perspective is Psychological Capital (PsyCap), a higher order construct that consists of the sub-dimensions: efficacy, hope, optimism, and resiliency. The overall aim of this thesis is to investigate the relationship between PsyCap and safety in HROs."/p" "p"The current study examines diverse empirical evidence to assess whether PsyCap could represent a potential antecedent to psychological safety climate and loss prevention across three different HROs (i.e., the aviation, shipping and offshore oil and gas industries). More specifically, possible mediators (i.e., positive/negative emotions and job satisfaction) and possible moderators (i.e., work role) of this relationship were examined in Papers 1 and 2. The influence of impression management and self-deception is controlled for in Paper 2, while the potential buffering effect of PsyCap on the relationship between worries about workplace risks and sleepiness is examined in Paper 3."/p" "p"The first study examined whether PsyCap is related to individual perceptions of safety climate in Air Traffic Control (ATC). The results from an all-Norwegian sample of about 25% of the population of Norwegian air traffic controllers showed that PsyCap was positively correlated with and explained almost 1/3 of the variance in perceived safety climate. In the second part of the study, the mediating effects of positive and negative emotions were controlled for, to see whether the respondents were “wearing rose tinted glasses” and answered the questions in an overly positive way. The results showed that neither positive nor negative emotions mediated the relationship between PsyCap and safety climate."/p" "p"The aim of the second study was to replicate and extend the findings from the ATC study in a new sample from a different type of HRO. Thus, the second study was conducted among maritime workers of different nationalities working for three Norwegian shipping companies. Again, the results showed that PsyCap was positively related to perceptions of safety climate. PsyCap contributed to the variance in perceived safety climate, even after adjusting for socially desirable responding. Officers with high scores on PsyCap were found to have a more positive perception of the safety climate than the non-officers with high PsyCap scores. In the second part of the study, a positive relation between perceived safety climate and job satisfaction was established, as well as between PsyCap and job satisfaction. A crossnational difference was discovered in the sample. An indirect effect of PsyCap with perceived safety climate through job satisfaction was valid only for European workers and not for Filipinos. Altogether, PsyCap and job satisfaction explained more than 20% of the variance in perceived safety climate."/p" "p"The third study shed light on PsyCap as a protective factor in a safety critical work environment. The relationship between worries about accidents and sleepiness was examined in a sample of offshore workers from different nationalities, in order to investigate whether PsyCap could represent a protective factor. The findings indicated a reverse buffering effect in that PsyCap only had a protective impact on sleepiness when worries about accidents were low. The established associations remained consistent after controlling for workers’ years of experience as seafarers and their ratings of perceived safety climate."/p" "p"In conclusion, this thesis extends the previous research by investigating the role of POB in safety. More precisely, it establishes empirical evidence suggesting that the behavioral dispositions of PsyCap are related to perceived safety climate across HROs from the aviation, offshore, and shipping industries. Thus, an increased emphasis on POB may present a new approach to increasing safety focus and loss prevention in these organizations. Future research should also investigate other HROs. Including PsyCap in the safety research could help create a better understanding of how people make work decisions based on their outlook on work and life in general. Although these results seem promising, more research is still needed, and this dissertation also addresses future research needs and the potential practical implications of these findings. Hopefully, there will be more research on PsyCap and safety aimed at preventing accidents in HROs.