Distributions of travel time variability on urban roads

Reliability is an important factor in route, mode and also departure time choice analysis and is a key performance indicator for transport systems. However, the current metrics used to measure travel time variability may be not sufficient to fully represent reliability. Better understanding of the distributions of travel times is needed for the development of improved metrics for reliability. A comprehensive data analysis involving the assessment of longitudinal travel time data for two urban arterial road corridors in Adelaide, Australia, demonstrates that the observed distributions are more complex than previously assumed. The data sets demonstrate strong positive skew, very long upper tails, and sometimes bimodality. This paper proposes the use of alternative statistical distributions for travel time variability, with the Burr Type XII distribution emerging as an appropriate model for both links and routes. This statistical distribution has some attractive properties that make it suitable for explicit definition of many travel time reliability metrics. Copyright © 2011 John Wiley & Sons, Ltd.     

A microscopic analysis of speed deviation impacts on lane-changing behavior

Driving behavior models that capture drivers’ tactical maneuvering decisions in different traffic conditions are essential to microscopic traffic simulation systems. This paper focuses on a parameter that has a great impact on road users’ aggressive overtaking maneuvers and directly affects lane-changing models (an integral part of microscopic traffic simulation models), namely, speed deviation. The objective of this research is to investigate the impacts of speed deviation in terms of performance measures (delay time, network mean speed, and travel time duration) and the number of lane-change maneuvers using the Aimsun traffic simulator. Following calibration of the model for a section of urban highway in Tehran, this paper explores the sensitivity of lane-changing maneuvers during different speed deviations by conducting two types of test. Simulation results show that, by decreasing speed deviation, the number of lane changes reduces remarkably and so network safety increases, thus reducing travel time due to an increase in network mean speed.     

Characteristics of speed dispersion and its relationship to fundamental traffic flow parameters

Speed dispersion is essential for transportation research but inaccessible to certain sensors that simply record density, mean speed, and/or flow. An alternative is to relate speed dispersion with these available parameters. This paper is compiled from nearly a quarter million observations on an urban freeway and a resulting data-set with two speed dispersion measures and the three fundamental parameters. Data are examined individually by lane and aggregately by direction. The first dispersion measure, coefficient of variation of speed, is found to be exponential with density, negative exponential with mean speed, and two-phase linear to flow. These empirical relationships are proven to be general for a variety of coefficient ranges under the above function forms. The second measure, standard deviation of speed, does not present any simple relationships to the fundamental parameters, and its maximum occurs at around a half to two-thirds of the free flow speed. Speed dispersion may be significantly different by lane.     

Restructuring the Greek Railways: Current Progress and Evaluation of Alternative Schemes

Abstract

This paper presents the rationale, the method, and the alternative choices in the process of restructuring the Hellenic Railways Organisation (OSE). The most likely alternative structures regarding ownership and management issues of the new entities that will inherit the old OSE organization, and discusses the strategic implications of these alternatives are discussed. A critical view of the process of Greek railway reform and the evaluation results of the alternative organizational structures for the new situation are presented. It first presents the current experience in European Union and other countries of Europe, and the relative position of the Greek railways vis‐à‐vis the most common practices. The most likely options for the new organizational structure are presented which will result from the application of the European Union Directives and the Greek Law 2671/98 for the reorganization of the Greek railways. Based on a more detailed presentation of expected income and expenditures (i.e. economic viability) of the alternatives, a structure and a roadmap to these reforms is recommended for a successful and, above all ‘implementable’, reform of the Greek railways under the current conditions. Finally, the process for change and restructuring is described in terms of the basic principles and procedures that should be followed, and in terms of the necessary steps and procedures for the transition from the current to the new situation.     

Enablers and Barriers to the Adoption of Alternatively Powered Buses

Abstract

This paper seeks to identify enablers and barriers that stimulate or prevent the adoption of alternatively powered buses (APBs) in cities. The research method concentrates on an in‐depth analysis of 21 European demonstration case studies of APBs. Considerable differences exist between these cities due to the different reference situation. The type of measurement and the situation in the demonstration cities influence the exact fuel consumption and emission reduction. Variables that could enable the adoption of all types of APBs are: (1) the compatibility with previously introduced ideas; (2) the already available necessary supporting infrastructure in the city; (3) a changed external appearance of the APB; (4) the acceptance of the APBs by passengers and bus drivers; and (5) political support in the city regarding the APBs. The main variables that could be determined as barriers are: the relative economic advantage (the outline of costs is higher than that of conventional buses); and the understanding of the APB for bus drivers and mechanics (because special training is needed for both groups).     

Contingency Planning and War Gaming for the Transport Operations of the Athens 2004 Olympic Games

Abstract

Transport operations constitute a critical prerequisite for the successful staging of a special event. Operations are more challenging to manage for those events that are infrequent and last for several days. In this case, the requirements for unconditional success, coupled with the uncertainties involved, necessitate robust contingency planning. The paper presents a methodological process for developing the transport‐related contingency plans to address pre‐identified emergencies in major events, such as the Olympic Games. War games are proposed to test the resulting contingency plans and train the staff involved in plan implementation. The application of the methodological process to the Athens 2004 Athens 2004 Organizing Committee (ATHOC). 2002. Preliminary Olympic Transport Strategic Plan, Athens: ATHOC.  [Google Scholar] Olympic Games is presented in which transport services were offered to over 50 000 members of the Olympic Family, 150 000 staff and volunteers, and 3.8 million spectators over a period of more than two weeks.     

External Costs of Domestic Container Transportation: Short‐Sea Shipping versus Trucking in Taiwan

Abstract

This paper explores the external costs of domestic container transportation in Taiwan by analysing the origin and destination of current container cargoes. After reviewing an extensive literature survey of methods of external cost, a comparison of external costs between trucking and short sea shipping (SSS) by corridor is made by using a model developed in this paper. Based on the findings that external costs of SSS are considerably lower than truck transport and can be a viable alternative to current domestic container cargo transportation, we discuss the significance and managerial implications of SSS from the perspective of green logistics. In so doing, a top‐down approach is employed for developing government policies, which aim to not only reduce the external costs of domestic container transportation but also promote SSS in Taiwan.     

A Quantitative Analysis of the Performance of Transportation Projects in Developing Countries

Abstract

This paper presents the results of a detailed quantitative analysis of performance metrics of a sample consisting of 89 transportation projects sponsored by the World Bank. The sample and a subset consisting of 65 projects were evaluated using the performance metrics of project cost, schedule and scope. The effect of project size (dollar value) and project duration on performance metrics was investigated. Also, the achievement of project goals and potential improvement in planning and estimating over time (the learning effect) was studied. It was found that, in general, in transportation projects sponsored by the World Bank, costs are overestimated and schedules are optimistic. The outcome with respect to cost seems counter‐intuitive because previous work by other researchers had shown a systematic underestimation of project costs. There is significant evidence that there are no efficient controls in place to predict or prevent schedule delays. The study also showed that during the past 15 years, no improvement (learning effect) was evident in project cost and duration estimation as the level of accuracy has not changed significantly. Further, it is observed that project duration did not affect the performance with respect to cost and delay.     

Effect of number of wheels on high speed UGV traversability: Online terrain assessment approach

This paper addresses the problem of determining the maximum allowable speed (V _max ) of Unmanned Ground Vehicles (UGVs) traversing off-road heterogeneous rough/complex terrain. The maximum speed is calculated based on online terrain assessment and the vehicle’s characteristics; this speed achieves the high speed navigation without exceeding a predefined allowable range of transmitted force and moments (i.e., moments in the roll and pitch directions) to the vehicle’s frame. The proposed system enables UGV’s to change their speed autonomously and transit between terrains with different characteristics (e.g., pavement, rocky) safely. This paper proposes a computationally inexpensive approach to process acquired data and assess the terrain roughness. The proposed Roughness Index (RI) is used to represent the terrain roughness on a scale from 0.0 (highly rough to be traversed by a particular vehicle) to 1.0 (perfectly flat/smooth surface). A general vehicle model (workable for any vehicle size and wheel configuration) is presented in this paper. A closed form expression of the maximum allowable vehicle speed is developed. Simulation results obtained on real vehicles (e.g., military tank LEOPARD I) show the effect of increasing the number of wheels to improve the capability of a ground vehicle to traverse rough terrains at high speeds. In addition, the proposed terrain assessment system is a key module in UGVs navigation systems enabling them to be truly autonomous by providing the navigation system with the necessary information for path and speed planning.     

Robust design optimization of suspension system considering steering pull reduction

This paper presents robust design optimization method to reduce steering pull phenomenon. One of the biggest causes of steering pull phenomenon is tolerance of suspension system such as hard point, spring, damper and bush. Therefore, the relationship between suspension systems and steering pull phenomenon has as nonlinear characteristics. But, it can be very difficult to evaluate the analytical design sensitivity. Thus, it is impossible to directly apply a well-developed optimization algorithm based on gradient information. To avoid these difficulty, this study uses sequential approximation optimization process based on a meta-model. The robust design process has 28 random design variables with tolerance. For efficient design process, the sample variances for the design goals are approximated from meta-models. The proposed approach required only 62 evaluations until it converged. Optimal design reduced the drift by 80% and its deviation by 38.7%, respectively. This result proves that the suggested design method of suspension system is effective and useful.