Exact Equations for Tractrix Curves Associated with Vehicle Offtracking

Vehicle offtracking behavior at low speeds is closely approximated by a geometric entity called a tractrix. This paper presents differential equations for generalized coordinates of a planar multibody vehicle model based on tractrix behavior. The equations are exact, can be used with any type of input path, are valid for forward and backward movements, and are much simpler than previously published formulations used to compute transient offtracking. The differential equations can be integrated using conventional numerical integration algorithms to obtain plots of the low-speed tracking performance of articulated vehicles. The equations were formulated symbolically by a computer program used to analyze the kinematic and dynamic behavior of multibody systems. Example numerical results are plotted.     

Development and Deployment of Public Transport Policy and Planning in Taiwan

Over the past decade, the escalating roadway congestion and environmental deterioration due to heavy use of private vehicles have provoked the Taiwan government to realize the importance of public transport systems. Under the “carrot-and-stick” rationales, the government has formulated public transport policies and exercised a series of related initiatives by providing sufficient and higher quality of public transport services so as to attract more private vehicle users. In this paper, the planning philosophy and policy formulation of Taiwan’s public transport development are highlighted. The most important initiatives, including the Five-year Enhancement of Mass Transportation Program and the upgrading public transport schemes in the National Development Plan are examined. Based on previous experience and lessons, we point out the most challenging issues that the government will encounter. Suggestions for the future of public transport planning are also addressed.     

Should the user pay?

The paper puts the case that historical analysis helps to understand current discussions on user-pays principles and practice. In particular, (a) it is demonstrated that the nature of funding systems is dominated by political considerations, and (b) user-pays systems lead to inadequate funding of infrastructure when politically controlled, but provide funds for expansion when “market-driven” (in pursuit of profit maximisation). The case is illustrated by reference to the experience of interregional transport infrastructure in 19th century in England and 20th century Australia. Revenue deficiencies arising from government-controlled rates can lead to the demise of private transport infrastructure. The problem is considered in the context of the history of interregional roads and railways in England between the 15th and 19th century in England and in Australia in the 19th and 20th century. The current embrace by government of the user-pays system in transport services arises from fiscal deficiencies, as much from economic philosophy. User-pays policies are part of the global re-emergence of economic rationalism since the 1970s. The lesson for other nations from Australia's experience is twofold. First, in a federal system of government, despite the efficiency benefits of user-pays in interregional land transport, fiscal and political objectives will prevail. Second, in sparsely populated and/or developing countries, deregulation of long distance road transport will make funding a national highway system a critical concern.     

Effects of information in road transport networks with recurrent congestion

This paper aims to gain more insight into the implications of information provision to drivers on the performance of road transport networks with recurrent congestion. For this purpose, a simulation program consisting of three components has been written. The first component is the traffic simulation model, the second component is the information provision mechanism, and the third component monitors the behavioural decision-making process of the drivers, which is modelled using a utility-based satisficing principle. Three types of information provision mechanisms will be considered: information based upon own-experience, after-trip information and real-time en route information. The findings in this paper, obtained in a hypothetical context, underline the important relationship betweenoverreaction, thelevel of market penetration and thequality of the information. High quality information allows a high level of market penetration, while low quality information, even when provided at low levels of market penetration, induces overreaction. Furthermore, real-time en route information is in particular beneficial during the process leading to a steady state; it reduces the variance in travel time considerably. The paper concludes with a discussion on the market potential of motorist information systems when commercially marketed.     

Effect of capacity concentration on highway corridor performance

This paper investigates, through use of analytical models, the effects of capacity concentration on highway corridor performance. It concludes that when highways operate at a fixed total capacity, decreasing the highway spacing can increase the average travel time because highways will become more congested. When highways operate below capacity, decreasing the spacing is usually beneficial as it tends to reduce trip length when accessing highways, and allows a greater percentage of travel to be completed on highways instead of arterials.     

Hybrid Electric Drive for DDG-51 Class Destroyers

The first of the Arleigh Burke class destroyers is nearing its mid-life. This class of ships was designed during the late 1970s through the 1980s to meet the threats that were prevalent at that time. Since entering service in 1991, these ships have shown themselves to be extremely versatile and the class now consists of nearly 60 ships in service. Their combat systems have been continually upgraded and adapted to meet the new threats the United States faces today. However, in order to keep these platforms viable throughout the first half of the 21st century, their operating costs must be reduced. Manpower, maintenance, and fuel are three of the top operating cost drivers. Most surface combatants spend very little of their underway time operating at full speed or even close to that. Over 1/3 of their underway time is spent at 12 knots and under. This is less than half of their maximum speed and only a fraction of the maximum power owing to the cubic speed–power relationship. Although the existing mechanical drive system is reasonably efficient, the main gas turbines are extremely inefficient at these very low power levels. A shaft-mounted auxiliary electric propulsion system (EPS) can take advantage of excess capacity in the ship service generators to reduce the main engine operating hours. Enabling bi-directional power flow from this auxiliary electric drive will provide additional generation capacity for ship service loads at a modest additional cost. It also provides a "cross-connect" capability from one shaft to the other. This paper will explore one prospect for reducing the operating cost of the DDG-51 class of ships by installing an auxiliary EPS that would powered by the ship service electrical plant. This additional system would serve to reduce both underway fuel usage as well as maintenance on the gas turbine main engines by reducing the number of operating hours on each engine. We will examine the technology trade-offs in this ongoing study.     

Introduction: Habitual travel choice

In this introduction to the special issue on habitual travel choice, we provide a brief account of the role of habit in travel behaviour, discuss more generally what habitual choice is, and briefly review the issues addressed in the solicited papers. These issues include how habitual travel behaviour should be measured, how to model the learning process that makes travel choice habitual, and how to break and replace car-use habits.     

Habitual travel behaviour: Evidence from a six-week travel diary

This paper introduces different methods to measure similarity of travel behaviour addressing the question of how repetitious travel behaviour actually is. It compares empirical results of the different methods based on the data from a six-week travel diary. In general, the results show that the day-to-day behaviour is more variable if measured with trip-based methods instead of methods based on time budgets. Furthermore, it is confirmed that the similarity declines if the method captures more of the complexity of the travel pattern. It is also shown that travel behaviour is neither totally repetitious nor totally variable. Even for the whole observation period, it is demonstrated that two days always have some common elements. Additionally, it is found that the different methods yield the same pattern of variability for different types of day. Travel behaviour is clearly more stable on work days. Similar results for all methods are also obtained concerning the question of how long the minimum period of observation should be. All measures show that the period should not be less than two weeks if one aims at measuring variability.