Modeling intermodal equilibrium for bimodal transportation system design problems in a linear monocentric city

This paper investigates the intermodal equilibrium, road toll pricing, and bus system design issues in a congested highway corridor with two alternative modes - auto and bus - which share the same roadway along this corridor. On the basis of an in-depth analysis of the demand and supply sides of the bimodal transportation system, the mode choice equilibrium of travelers along the continuum corridor is first presented and formulated as an equivalent variational inequality problem. The solution properties of the bimodal continuum equilibrium formulation are analytically explored. Two models, which account for different infrastructure/system regulatory regimes (public and private), are then proposed. In the public regulatory model, the road toll location and charge level are simultaneously optimized together with the bus service fare and frequency. In the private regulatory model, the fare and frequency of bus services, which are operated by a profit-driven private operator, are optimized for exogenously given toll pricing schemes. Finally, an illustrative example is given to demonstrate the application of the proposed models. Sensitivity analysis of residential/household distribution along the corridor is carried out together with a comparison of four different toll pricing schemes (no toll, first best, distance based, and location based). Insightful findings are reported on the interrelationships among modal competition, market regulatory regimes, toll pricing schemes, and urban configurations as well as their implications in practice.     

Diesel hybrid electric vehicle hardware system

A controller for a diesel hybrid electric vehicle based on a V-cycle development approach is investigated in this paper. The hardware and infra program of the Hybrid Control Unit (HCU) are discussed in detail. The hardware system is designed based on circuit simulation; while the infra system is written with assemble language. Time sharing mode, buffer sharing mode and multi-task schedule method are used to ensure real-time communication in the infra program design. Based on multi-thread technology, hardware in loop test system is also designed. The hardware in loop and bench tests show that the controller could meet the requirements of the hybrid electric vehicle (HEV) and communicate in real-time. Circuit simulation, HCU, infra program and hardware in loop test form the effective V-cycle development platform to design a hardware system for a diesel HEV controller.     

Dependence of fatigue limit of high-tension bolts on mean stress and ultimate tensile strength

High tension bolts in critical joints in internal combustion engines are susceptible to fatigue failure. Computeraided bolted joint design procedures require knowledge of the dependence of bolt fatigue limit on the mean stress and ultimate tensile strength. This dependence is investigated with staircase fatigue limit tests. The test results show that when the bolt fatigue limit is estimated with the nominal stress of the bolt, it decreases with increasing tensile strength and nominal mean stress. However, there is a range of the nominal mean stress where the bolt fatigue limit is almost constant. The test results are interpreted with finite element analysis.     

沥青层应变传感器数据采集及处理方法研究

介绍了沥青路面电阻应变传感器的基本原理,分析了数据采集过程中初始电压达到极限状态的原因和调整方法,通过试验分析确定了高速车轮荷载和FWD荷载作用下应变传感器数据采集系统的合理采集频率,最后结合应力应变传感器在动态荷载作用下的响应规律,总结了将电阻应变传感器电压信号转换为应变信号的数据处理方法.     

Does scale heterogeneity across individuals matter? An empirical assessment of alternative logit models

There is growing interest in establishing a mechanism to account for scale heterogeneity across individuals (essentially the variance of a variance term or the standard deviation of utility over different choice situations), in addition to the more commonly identified taste heterogeneity in mixed logit models. A number of authors have recently proposed a model that recognizes the relationship between scale and taste heterogeneity, and investigated the behavioural implications of accounting for scale heterogeneity in contrast to a term in the utility function, itself. In this paper we present a general model that extends the mixed logit model to explicitly account for scale heterogeneity in the presence of preference heterogeneity, and compare it with models that assume only scale heterogeneity (referred to as the scale heterogeneous multinomial logit model) and only preference heterogeneity. Our empirical assessment suggests that accommodating scale heterogeneity in the absence of accounting for preference heterogeneity may be of limited empirical interest, resulting in a statistically inferior model, despite it being an improvement over the standard MNL model. Scale heterogeneity in the presence of preference heterogeneity does garner favour, with the generalized mixed logit model an improvement over the standard mixed logit model. The evidence herein suggests, however, that compared to a failure to account for preference heterogeneity that is consequential, failure to account for scale heterogeneity may not be of such great empirical consequence in respect of behavioural outputs such as direct elasticities and willingness to pay. However additional studies are required to establish the extent to which this evidence is transferable to a body of studies.     

Development of a delay model for unsignalized intersections applicable to traffic assignment

Abstract

This paper develops a model for estimating unsignalized intersection delays which can be applied to traffic assignment (TA) models. Current unsignalized intersection delay models have been developed mostly for operational purposes, and demand detailed geometric data and complicated procedures to estimate delay. These difficulties result in unsignalized intersection delays being ignored or assumed as a constant in TA models.

Video and vehicle license plate number recognition methods are used to collect traffic volume data and to measure delays during peak and off-peak traffic periods at four unsignalized intersections in the city of Tehran, Iran. Data on geometric design elements are measured through field surveys. An empirical approach is used to develop a delay model as a function of influencing factors based on 5- and 15-min time intervals. The proposed model estimates delays on each approach based on total traffic volumes, rights-of-way of the subject approach and the intersection friction factor. The effect of conflicting traffic flows is considered implicitly by using the intersection friction factor. As a result, the developed delay model guarantees the convergence of TA solution methods.

A comparison between delay models performed using different time intervals shows that the coefficients of determination, R ², increases from 43.2% to 63.1% as the time interval increases from 5- to 15-min. The US Highway Capacity Manual (HCM) delay model (which is widely used in Iran) is validated using the field data and it is found that it overestimates delay, especially in the high delay ranges.     

Vertical Vibration Analysis of Vehicle/Imperfect Track Systems

Summary This paper studies the vertical vibration of a vehicle traveling on an imperfect track system. The car body and sleepers are modeled as Timoshenko beams with finite length, and the rail is assumed as an infinite Timoshenko beam with discrete supports. Imperfection of the track system comes from a sleeper lost partial support by the ballast. Since deflection of the rail is limited within a certain interval where the vehicle is passing over, the infinite domain problem can be transformed into a finite domain problem with moving boundary. In this work, the equations of motion of the car body, rail and sleepers are discretized first by the finite element method. The discretized equations of motion for the vehicle and track systems are then assembled, respectively. Finally, the Newmark method is applied to obtain the response of the vehicle and track systems at each time step. The effect of the vehicle speed on the response of the vehicle and track systems is investigated.     

Optimization of blending oil with non-esterified biodiesel fuel using design of experiment at partial engine loads

Non-esterified bio-diesel fuel is more economically feasible than esterified one because of simple manufacturing process that only consists of filtering. Applicability of this fuel on diesel engine with electronic control system was tried and accomplished in a previous research. In this study, optimization adopting a fractional factorial design and response surface methodology was carried out at 25 % and 50 % of engine load in order to verify effectiveness of design of experiment for performance optimization of diesel engine. Pcr and IT mainly affected responses as specific fuel oil consumption and nitrogen oxides regardless of engine load according to the fractional factorial design. Estimations were 310.3 g/kWh of specific fuel oil consumption and 237 ppm of nitrogen oxides at 25 % load, and 233.2 g/kWh of specific fuel oil consumption and 730 ppm of nitrogen oxides at 50 % load according to the response surface methodology. As the results of verification tests, specific fuel oil consumption and NOx were respectively 300.4 g/kWh and 277 ppm at 25 % load, and 236.8 g/kWh and 573 ppm at 50 % load. Since there were small differences between estimations and verifications, adopting Box-Behnken method of the response surface methodology for performance optimization of diesel engine should be considered carefully.     

Chevrolet Volt on-road test programs in Canada part 1: Effects of drive cycle,ambient temperature and accessory usage on energy consumption and all-electric range

Environment Canada (EC) and Natural Resources Canada (NRCan) separately tested two 2012 Chevrolet Volts between 2013 and 2014 in Ottawa, Ontario on public roads in the summer and winter months using realistic cabin-climate control settings. More than 1300 trips were conducted over nine routes: three city, one congested, two arterial, one highway and two expressway routes. EC tests recorded cabin conditioning, traction battery and 12 V accessory power, select vehicle component temperatures, regulated emission rates and exhaust flow, and DC charge energy. Both NRCan and EC tests measured cumulative electrically driven distance (all-electric range), select CANbus signals and AC grid supply charge energy. Results from these studies were analysed to evaluate the overall performance of the Chevrolet Volt on public roads in climates representative of most of Canada (-27 °C to 37 °C) using realistic accessory settings. At 25 °C the Chevrolet Volt’s on-road all-electric EPA-method adjusted range is generally less than the U.S. EPA sticker rating (57.9 km). Cabin conditioning energy was found to be directly related to the difference between ambient and cabin temperature, except at low temperatures (< 0 °C) when the 1.4 L engine activates to assist the thermal management system. On average, heating the cabin in the winter months consumed significantly more electric energy than cooling the cabin in the summer months. Summer city and highway driving resulted in the lowest energy consumption (Wh/km), while congested and expressway driving cycles resulted in the highest. In the winter months, many differences between the drive cycles were not discernible due to the high cabin conditioning energy consumptions.     

Effects of altitude on combustion characteristic during cold start of heavy-duty diesel engine

Altitude has a significant effect on combustion of heavy-duty diesel engines, especially during cold start. An experimental study on a heavy-duty diesel engine operating at different altitudes was conducted. Tests were based on a direct injection (DI) turbocharged diesel engine with intake and exhaust pressure controlled by the plateau simulation test system to stimulate altitude conditions including 0 m, 1000 m, 2000 m, 3000 m and 4000 m. Results indicated that the compression and expansion resistance moment reduced and the speed increased during the cranking period. The peak pressure of several cycles was increased during the start-up period; however, the expansion pressure dropped more and the indicated mean effective pressure (IMEP) reduced as the altitude rose. While at an altitude of over 2000 m, the peak pressure fluctuated obviously during the start-up period. The higher the altitude was, the more the fluctuation amplitude and cycle number increased and combustion instability enhanced, which resulted the start-up period time increasing at high altitude. When the altitude rose, the cycle-to-cycle variation of the peak pressure and speed fluctuation increased during the idle, the ignition and CA50 were delayed and the combustion duration was shortened. The effect of altitude on combustion characteristics of the diesel engine was more significant during the start-up period than during its idle period.