Studying travel-related individual assessments and desires by combining hierarchically structured ordinal variables

Ordinal measures are frequently encountered in travel behavior research. This paper presents a new method for combining them when a hierarchical structure of the data can be presumed. This method is applied to study the subjective assessment of the amount of travel by different transportation modes among a group of French clerical workers, along with the desire to increase or decrease the use of such modes. Some advantages of this approach over traditional data reduction technique such as factor analysis when applied to ordinal data are then illustrated. In this study, combining evidence from several variables sheds light on the observed moderately negative relationship between the personal assessment of the amount of travel and the desire to increase or decrease it, thus integrating previous partial (univariate) results. We find a latent demand for travel, thus contributing to clarify the behavioral mechanisms behind the induced traffic phenomenon. Categorizing the above relationship by transportation mode shows a desire for a less environmental-friendly mix of modes (i.e., a greater desire to use heavy motorized modes and a lower desire to use two-wheeled modes), whenever the respondents do not feel to travel extensively. This result, combined with previous theoretical investigations concerning the determinants of the desire to alter trips consumption levels, shows the importance of making people aware of how much they travel.

Low temperature premixed combustion within a small bore high speed direct injection (HSDI) optically accessible diesel engine using a retarded single injection

An optically accessible single-cylinder high speed direct-injection (HSDI) Diesel engine equipped with a Bosch common rail injection system was used to study low temperature Modulated Kinetics (MK) combustion with a retarded single main injection. High-speed liquid fuel Mie-scattering was employed to investigate the liquid distribution and evolution. By carefully setting up the optics, three-dimensional images of fuel spray were obtained from both the bottom of the piston and the side window. The NOx emissions were measured in the exhaust pipe. The influence of injection pressure and injection timing on liquid fuel evolution and combustion characteristics was studied under similar fuel quantities. Interesting spray development was seen from the side window images. Liquid impingement was found for all of the cases due to the small diameter of the piston bowl. The liquid fuel tip hits the bowl wall obliquely and spreads as a wall jet in the radial direction of the spray. Due to the bowl geometry, the fuel film moves back into the central part of the bowl, which enhances the air-fuel mixing process and prepares a more homogeneous air-fuel mixture. Stronger impingement was seen for high injection pressures. Injection timing had little effect on fuel impingement. No liquid fuel was seen before ignition, indicating premixed combustion for all the cases. High-speed combustion video was taken using the same frame rate. Ignition was seen to occur on or near the bowl wall in the vicinity of the spray tip, with the ignition delay being noticeably longer for lower injection pressure and later injection timing. The majority of the flame was confined to the bowl region throughout the combustion event. A more homogeneous and weaker flame was observed for higher injection pressures and later injection timing. The combustion structure also proves the mixing enhancement effect of the liquid fuel impingement. The results show that ultra-low sooting combustion is feasible in an HSDI diesel engine with a higher injection pressure, a higher EGR rate, or later injection timing, with little penalty on power output. It was also found that injection timing has more influence on HCCI-like combustion using a single main injection than the other two factors studied. Compared with the base cases, simultaneous reductions of soot and NOx were obtained by increasing EGR rate and retarding injection timing. By increasing injection pressure, NOx emissions were increased due to leaner and faster combustion with better air-fuel mixing. However, smoke emissions were significantly reduced with increased injection pressure.     

Happy today,satisfied tomorrow: emotion—satisfaction dynamics in a multi-week transit user smartphone survey

Transportation - Travel well-being encompasses three dimensions: cognitive satisfaction judgments, positive emotions, and negative emotions. Most previous literature on transit users focused either...     

Why (not) abolish fares? Exploring the global geography of fare-free public transport

Transportation - Although the policy of abolishing fares in public transport—here referred to as “fare-free public transport” (FFPT)—exists in nearly 100 localities...     

水平小净距隧道中夹岩安全系数法研究与应用北大核心CSCD

中夹岩柱是小净距隧道围岩稳定控制的关键部位,判别中夹岩的安全性是工程设计和施工过程中的重难点。文章通过分析不同围岩级别、埋深情况下中夹岩的破坏模式,建立Ⅳ级围岩条件下水平小净距隧道中夹岩力学分析模型,并确定中夹岩破裂面位置。根据中夹岩上部滑块体形状的不同分为两种情况,通过边坡稳定性原理、极限平衡假设及普氏压力拱理论推导中夹岩上部滑块体的抗滑力、下滑力以及安全系数的计算公式,从而建立起评判中夹岩安全性的安全系数法,并结合数值模拟对其进行验证。将经验证后的安全系数法应用于某实际隧道工程,判断其中夹岩安全性,得出该隧道中夹岩破坏临界厚度为6 m,进而对6 m以下的中夹岩使用锚杆进行加固。     

The influence of built environment to the trends in commuting journeys in the Netherlands

In this paper we describe commuting trends in the Netherlands in the past decade and examine the influence of urban form and travel accessibility on commuting journeys over time on the basis of data from the Dutch National Travel Survey. Exploratory analysis is performed to identify changes in commuting participation, departure time, commuting time, commuting distance and the modal split. Regression analysis and choice models are used to examine the influence of the built environment on commuting parameters over time. The results indicate that urban form has consistently influenced the parameters of commuting journey in the Netherlands in the last 10 years. However, the trend of the influence is unique for each commuting model. Some influences have become less significant in the last decade and some have become stronger.

Information impact on quality of multimodal travel choices: conceptualizations and empirical analyses

This paper investigates the impact of a variety of travel information types on the quality of travel choices. Choice quality is measured by comparing observed choices made under conditions of incomplete knowledge with predicted choice probabilities under complete knowledge. Furthermore, the potential impact of travel information is considered along multiple attribute-dimensions of alternatives, rather than in terms of travel time reductions only. Data is obtained from a choice experiment in a multimodal travel simulator in combination with a web-based mode-choice experiment. A Structural Equation Model is estimated to test a series of hypothesized direct and indirect relations between a traveler’s knowledge levels, information acquisition behavior and the resulting travel-choice quality. The estimation results support the hypothesized relations, which provides evidence of validity and applicability of the developed measure of travel-choice quality. Furthermore, found relations in general provide some careful support for the often expected impact of information on the quality of travel choices. The effects are largest for information services that generate previously unknown alternatives, and lowest for services that provide warnings in case of high travel times only.

A “rutter for piracy” in 2012

This "rutter for piracy" begins with a brief update on contemporary piratical incidents and a short review of books and collections of articles dedicated to the topic of piracy, before presenting the ground-breaking group of scholarly essays which make up WMU Journal of Maritime Affairs' special issue on piracy at sea.     

Shifting control of an automated mechanical transmission without using the clutch

The automated mechanical transmission (AMT) is gaining popularity in the automotive industry, due to its combination of the advantages of mechanical transmissions (MT) and automatic transmissions (AT) in terms of fuel consumption, low cost, improved driving comfort and shifting quality. However, the inherent structural characteristics of the AMT lead to disadvantages, including excessive wear of the clutch plates and jerk and traction interruption during the shift process, that severely affect its popularity in the automatic transmission industry. The emerging technology of shifting control without the use of the clutch is a promising way to improve the shifting transients of AMTs. This paper proposes a control algorithm that combines speed and torque control of the AMT vehicle powertrain to achieve shifting control without using the clutch. The key technologies of accurate engine torque and speed control and rapid position control of the shift actuators are described in detail. To realize accurate engine speed control, a combined control algorithm based on feed-forward, bang-bang and PID control is adopted. Additionally, an optimized closed-loop position control algorithm based on LQR is proposed for the shift actuators. The coordinated control algorithm based on engine and shift actuator control is described in detail and validated on a test vehicle equipped with an AMT. The results show that the coordinated control algorithm can achieve shifting control without the use of the clutch to improve driving comfort significantly, reduce shift transients and extend the service life of the clutch.     

Numerical investigation of a DI diesel spray flame using a detailed chemical reaction mechanism

Emission standards have grown increasingly stricter, consequently triggering greater interest in issues surrounding environmental pollution. In particular, soot and NOx released from DI diesel vehicles is considered to be the main source of air pollution in urban environments. However, the mechanics of fuel spray formation and the influence of the operating parameters on the resulting spray flame are not yet fully understood. In this study, the original KIVA code was modified to incorporate a detailed chemical reaction mechanism involving various species and multiple reaction steps to better understand the spray characteristics. n-Heptane, C₇H₁₆, was used as the representative fuel for diesel fuel, and the reaction mechanism for this fuel was composed of 66 species and 274 elementary reaction steps. The accuracy of the predicted results was demonstrated primarily by a comparison with experimental results. The numerical prediction of a specific operating condition for the parametric investigation correlates well with the experimental results.