Comparing static and dynamic threshold based control strategies

This research extends a static threshold based control strategy used to control headway variation to a dynamic threshold based control strategy. In the static strategy, buses are controlled by setting a threshold value that holds buses at a control point for a certain amount of time before allowing the bus to continue along the route. The threshold remains constant each time the bus stops at the control point. The dynamic strategy involves the same principle of holding buses at a bus stop; however, a different threshold value is chosen each time the bus holds at a control point. The results indicate that in cases where the static threshold is set equal to the scheduled headway, very low headway variation and passenger system times result; however, passengers on board the bus are penalized by extra delay on the bus while waiting at the control point. The dynamic strategy reduces the penalty to passengers delayed on-board the bus at a control point at the expense of a slight increase in overall passenger system time.The results indicate that in most cases, the tradeoff of the slight increase in waiting time for the significant decrease in on-board delay penalty makes the dynamic strategy an acceptable choice.     

Substitution between working at home and out-of-home: The role of ICT and commuting costs

This paper analyzes the trade-off between working at home and out-of-home, ICT and commuting time. To this end, we develop a microeconomic demand system, which explicitly incorporates both time and income constraints. Commuting time is considered as the price to be paid for working out-of-home and a decrease in earnings as the price for working at home. For the latter, we find that working at home leads to a (marginally significant) reduction of the wage rate of about 19%, but this gap largely disappears when ICT is used for at home work. To examine the relation between out-of-home and at home work empirically, we estimate a translog indirect utility function, from which we are able to estimate substitution and price elasticities between working at home and out-of-home for The Netherlands. The results show that changes in ICT and commuting time display rather weak substitution effects on working out-of-home and at home, respectively. Moreover, individual characteristics – especially age and education – seem to be more important for the choice between working at home and out-of-home than ICT availability or commuting time.     

Dispatching control at transfer stations in multi‐hub transit networks

Among dispatching control approaches, the holding option has attracted the most attention in bus control. However, holding a vehicle at a transfer station may exacerbate the delays because more passengers might accumulate at downstream stations and may also affect other connecting routes at other transfer stations. Our problem is to minimize the total costs of dispatching ready vehicles at each transfer station along coordinated routes in a multi‐hub transit network. The total costs include the waiting cost for on‐board passengers, the missed connection costs for late arrival passengers at the subject transfer station and possible transfer costs at downstream transfer stations. We develop a heuristic algorithm to optimize the holding times based on real time information about late vehicles. The results show that ready vehicles should be held longer when the arrival variances of late vehicles are small or when many late connecting passengers are expected.     

Home charge timing choice behaviors of plug-in hybrid electric vehicle users under a dynamic electricity pricing scheme

This paper examines choice behaviors pertaining to the time at which users of plug-in hybrid electric vehicle with 24 km electric range charge their vehicles after arriving at home under a dynamic electricity pricing scheme. The following mutually exclusive alternatives are presented: no charging, charging immediately after arriving at home, charging at the cheapest time, and charging at other times. Four versions of a mixed logit model with unobserved heterogeneity are applied to panel data on vehicle usage from 9 households with 2226 observations in Toyota City. Estimation results suggest that users’ willingness to charge become stronger with increasing driving distance when the driving distance is less than the electric range of 24 km, while tend not to charge when the driving distance is longer than the electric range. Users who return home at the cheapest time or during the day are willing to charge immediately after arriving at home. Electricity prices significantly affect choices to charge at the cheapest time for all users, and stay-at-home mother users and users returning home in the evening tend to charge at the cheapest time. Users returning home in the evening also tend to charge at other times, and being accustomed to charge at a certain time increases the probability of charging at other times. In addition, considerable variations are found across individuals with respect to their preferences for charge timing alternatives as well as for electricity prices.     

Long-term behavior of particulate matters at urban roadside and background locations in Seoul,Korea

The concentrations of particulate matter, PM_2.5, PM₁₀, and TSP at an urban roadside and an urban background station are analyzed. Data collected over a 10 year period are analyzed. The concentrations of the particulates measured at the urban site are systematically larger than at the background station. The mean PM values at the former also exhibit a slight fall over the decade unlike those at the background station. Overall, the particulate matters at both locations are in an intermediate range of global level, e.g., approximately two times lower than those in other Asian regions but higher than in Europe.     

An equity‐based passenger flow control model with application to Hong Kong‐Shenzhen border‐crossing

Cross‐border passengers from Hong Kong to Shenzhen by the east Kowloon‐Canton Railway (KCR) through the Lo Wu customs exceed nearly 200 thousand on a special day such as a day during the Chinese Spring Festival. Such heavy passenger demand often exceeds the processing and holding capacity of the Lo Wu customs for many hours a day. Thus, passengers must be metered off at all entrance stations along the KCR line through ticket rationing to restrain the number of passengers waiting at Lo Wu within its safe holding capacity. This paper proposes an optimal control strategy and model to deal with this passenger crowding and control problem. Because the maximum passenger checkout rate at Lo Wu is fixed, total passenger waiting time is not affected by the control strategy for given time‐dependent arriving rates at each station. An equity‐based control strategy is thus proposed to equalize the waiting times of passengers arriving at all stations at the same time. This equity is achieved through optimal allocation of the total quota of tickets to all entrance stations for each train service. The total ticket quota for each train service is determined such that the capacity constraint of the passenger queue at Lo Wu is satisfied. The control problem is formulated as a successive linear programming problem and demonstrated for the KCR system with partially simulated data.     

Factors associated with home-based e-working and e-shopping in Nanjing,China

The widespread adoption of information and communication technology has facilitated frequent e-activities in people’s daily life. From the perspective of individual’s time use on e-working and e-shopping at home, this paper aims to enhance our understanding of the function of home beyond a living space for family life. Using a household survey of 608 full-time paid employees who conducted e-activities at home in Nanjing, China, we investigated the characteristics and patterns of home-based e-working and e-shopping. Only 7.9% of the respondents neither e-shopped nor e-worked at home. We find that the socio-demographic context, Internet use habits, attitudes towards e-working/e-shopping, and geographical accessibility have influenced the patterns of home-based e-working and e-shopping. The results indicate that the rich e-activities taking place at home have changed the time use at home and reinforced the function of home as a multifunctional hub.     

Safety impacts of signalized lane merge control at highway work zones

Lane closures due to highway work zones present many challenges to the goal of ensuring smooth traffic operations and a safe environment for both drivers and workers. Late merge behavior at a work zone closure is a dangerous behavior that impacts the traffic conflicts upstream of work zone closures. This paper analyzes the safety impacts of using a signalized lane control strategy at the work zone merge points. To achieve the objective of this research, a field study has been conducted at a highway work zone to collect traffic and driver behavior data, and a two-stage, simulation-based approach is used to analyze the safety impacts of implementing a signalized lane merge control strategy at the studied work zone. In the first stage, micro-simulation models are developed and calibrated based on field data to generate vehicle trajectories. In the second stage, the U.S. Federal Highway Administration’s Surrogate Safety Assessment Model is employed to identify potential conflicts under different traffic conditions. The paper concludes that a proposed signal control device could significantly reduce lane-change conflicts at work zone merge points. In addition, recommendations on the signal cycle length and timing splits are provided.     

The marginal social cost of headway for a scheduled service

This brief paper derives the marginal social cost of headway for a scheduled service, i.e. the cost for users of marginal increases to the time interval between departures. In brief we may call it the value of headway in analogy with the value of travel time and the value of reliability. Users have waiting time costs as well as schedule delay costs measured relative to their desired time of arrival at the destination. They may either arrive at the station to choose just the next departure or they may plan for a specific departure in which case they incur also a planning cost. Then planning for a specific departure is costly but becomes more attractive at longer headways. Simple expressions for the user cost result. In particular, the marginal cost of headway is large at short headways and smaller at long headways. The difference in marginal costs is the value of time multiplied by half the headway.     

Transportania as gulliver might have seen it

It is an honour to be asked to speak at this, the Silver Jubilee of the International Symposia in 1984, in the presence of a number who, unlike myself, were present at the first symposium at the General Motors Research Laboratories in 1959 - Gordon Newell, Martin Beckmann and, foremost of all, Robert Herman, whose work is to be recognized next week by the award of an Honorary Degree at the University of Karlsruhe. Because it is such an honour to be asked, I had no hesitation in accepting Professor Volmuller's invitation, several months ago - to address you with a causerie on a subject of my choice.     

深埋隧洞围岩应力分布与破坏机理

深埋隧洞围岩高应力破坏机理是研究深埋岩体力学特性和深埋地下工程实践中被关注的一个重要认识问题,深埋条件下围岩应力和围岩强度之间的矛盾更加复杂和典型,也成为认识问题的基本出发点。文章介绍了深埋隧洞开挖时不同部位围岩应力的变化路径;通过对比锦屏辅助洞出现的围岩破坏现象,分别论述了导致边墙松弛型破坏、应力集中部位的片帮破坏和岩爆破坏的围岩应力变化特征,在一定程度上解释了这些破坏的内在机理;并通过采用数值方法再现脆性围岩V型破坏形式,分析探讨了脆性围岩高应力破坏的局部化问题;指出了深埋岩石力学研究中的几个重要环节,如岩体力学特征的尺寸效应和应力路径效应等对准确认识深埋隧洞高应力破坏内在机理的重要意义。     

Crash analysis at intersections in the CBD: A survival analysis model

Enhancing the safety level of urban roads especially in CBDs is paramount. Due to a large number of intersections in what is usually a grid road system in the CBDs, we investigate crashes occurring in and around an intersection. The question of interest in this study is: does the nature of crashes at intersections differ from those of the roads at midblock? Stated more precisely, considering the intersection as a reference point, does the distance to the reference point (i.e. midblock locations on the roads) correlate with different types of crashes compared to that of the intersection? A right answer can lead traffic engineers and safety auditors to propose different safety measures at intersections and the midblock locations. As a pilot study, we collected the last 9 years crash data of the CBD of Melbourne, Australia. For the first time, we employ Survival Analysis models -including Exponential, Weibull, and Log-logistic- to investigate a space-dependent phenomenon (i.e. accidents at proximity to the intersection). Of the outcome, highlights are: (i) police presence at busy intersections during busy night outs and weekends highly improves the pedestrian safety (ii) raised crossings at midblock locations lower likelihood of crashes of pedestrians as well as cars, (iii) lighting conditions at intersections must be watched and kept at a high level. (iv) Severity, likelihood, and location have no known association with the level of congestion. In other words, safety is first, always and everywhere. The results can be of interest to traffic authorities and policy makers in reinforcing traffic calming measures in the cities. The codes developed in this study are made available to the research community to be used in further studies.     

An empirical evaluation of the travel impacts of teleconferencing

On February 20, 1986, the regular monthly meeting of the Southern California Association of Governments (SCAG) Transportation and Communications Committee was held as a two-way videoconference. Analysis of travel changes associated with the videoconference showed that vehicle miles traveled actually increased, compared to an average meeting held at the usual single location at SCAG offices. Although the average distance per person to the nearest teleconference site was 24% lower than the distance to the SCAG offices, the attendance at the teleconference was so much higher than average that total VMT was 29% higher than for a typical meeting held at SCAG.     

Distributed conflict-free cooperation for multiple connected vehicles at unsignalized intersections

Connected vehicles will change the modes of future transportation management and organization, especially at intersections. In this paper, we propose a distributed conflict-free cooperation method for multiple connected vehicles at unsignalized intersections. We firstly project the approaching vehicles from different traffic movements into a virtual lane and introduce a conflict-free geometry topology considering the conflict relationship of involved vehicles, thus constructing a virtual platoon. Then we present the modeling of communication topology to describe two modes of information transmission between vehicles. Finally, a distributed controller is designed to stabilize the virtual platoon for conflict-free cooperation at intersections. Numerical simulations validate the effectiveness of this method.     

Comparing and presenting city-level transportation CO2 emissions using GIS

In 2011, the European Pollutant Release and Transfer Register (E-PRTR) inventory of diffuse emissions became available, providing data on a range of atmospheric emissions at a 5 km resolution across Europe. The data are produced from spatially disaggregated emissions totals for countries, and must be validated before being used at a sub-national level. The UK government maintains a 1 km resolution emissions inventory based on a bottom-up methodology by which a validation is possible. The UK National Atmospheric Emissions Inventory data are used to assess at what geographic scale the new E-PRTR data might be most useful. This paper compares the two data sets and estimates city-level transportation CO₂ emissions for 149 EU cities. We find that at a functional boundary level the two datasets match well.     

海底混输管道内部状态完整性分析

为保证某混输海管的安全运营,通过建立混输海管多相流动模型和腐蚀模型,分析海管典型运行工况参数与设计取值,得出管道多相流动参数分布规律、腐蚀速率主要影响因素和总腐蚀情况。结果表明：海管入口立管底部压力最高;管内沿线温度总体逐渐降低,具有轻微波动;平管上坡段和入口立管段持液率较高;液体流速对该管道腐蚀速率的影响最显著;入口立管段底部腐蚀速率最大,且均大于设计取值;腐蚀速率设计取值偏小。     

Dynamic vehicular delay comparison between a police-controlled roundabout and a traffic signal

Effects of queues on motorists during rush hours are severe at intersections controlled by roundabouts. Traffic police are frequently used in order to optimize the traffic flow and to control queue length at such intersections. However, the question as to how efficient such system is, compared with traffic signal, is not clear from the dynamic delay point of view. In this study a criterion is being developed based on vehicular delays as the motorist join the queues and cross the stop-line. The adopted method avoids oversimplification of reality and prevents unrealistic assumptions. The data required for the study were mainly collected through video filming technique. The results, for a given set of geometric and traffic characteristics, indicate that both a police-controlled roundabout and a traffic signal act in a similar manner in terms of vehicular delay at a certain critical value. This critical value is considered to be the point of intersection between the curves representing traffic signal and roundabout on a delay–space diagram for the vehicles as they join the tail end of the queue until they cross the stop-line. Beyond the critical value, the effect of delays and buildup of queues at roundabouts will be excessive, compared to traffic signals. Before the critical value the delays at traffic signals are quite high compared to roundabouts. The study will assist the concerned authorities to operate the existing conditions, particularly the roundabouts, more efficiently. It will also be beneficial for the traffic planners and policy makers in making judicious decisions regarding control type at intersections.     

Heterogeneity among motorists in traffic-congested areas in southern California

Estimation of congestion costs, presumed to be one of the largest external costs of automobile travel, is typically based on a single value of time delay for motorists in metropolitan areas. However, the estimation may be wrong if the profiles of motorists are different at different times of day. This study uses a survival model to examine the demographic and socioeconomic profiles of motorists at different times of day at congested locations in southern California, by using on-road remote-sensing measurements and license plates images obtained in 2007 and 2008 by the California South Coast Air Quality Management District (SCAQMD). More than 80,000 vehicles were observed from fifteen selected study sites over fifteen days. Their plates, through anonymized registration records, revealed addresses at the census block group level, which have homogenous profiles by construction. Motorists’ profiles at different times of day display large variation, however, according to extended Cox model with a non-parametric baseline hazard, which is used to accommodate both the time-invariant and time-varying effects of the covariates. This study thus proposes a new approach to examine heterogeneity among motorists.     

Using non-real-time Automatic Vehicle Location data to improve bus services

Although real-time Automatic Vehicle Location (AVL) data is being utilised successfully in the UK, little notice has been given to the benefits of historical (non-real-time) AVL data. This paper illustrates how historical AVL data can be used to identify segments of a bus route which would benefit most from bus priority measures and to improve scheduling by highlighting locations at which the greatest deviation from schedule occurs. A new methodology which uses historical AVL data and on-bus passenger counts to calculate the passenger arrival rate at stops along a bus route has been used to estimate annual patronage and the speed of buses as they move between stops. Estimating the patronage at stops using AVL data is more cost-effective than conventional methods (such as surveys at stops which require much more manpower) but retains the benefits of accuracy and stop-specific estimates of annual patronage. The passenger arrival rate can then be used to calculate how long buses spend at stops. If the time buses spend at stops is removed from the total time it takes the bus to traverse a link, the remaining amount of time can be assumed to be the time the bus spends moving and hence the moving speed of the bus can be obtained. It was found that estimation of patronage and the speed of buses as they move between stops using AVL data produced results which were comparable with those obtained by other methods. However the main point to note is that this new method of estimating patronage has the potential to provide a larger and superior data set than is otherwise available, at very low cost.     

Effectiveness of red light cameras on the right‐angle crash involvement of motorcycles

Red light cameras (RLCs) have been used to reduce right‐angle collisions at signalized intersections. However, the effect of RLCs on motorcycle crashes has not been well investigated. The objective of this study is to evaluate the effectiveness of RLCs on motorcycle safety in Singapore. This is done by comparing their exposure, proneness of at‐fault right‐angle crashes as well as the resulting right‐angle collisions at RLC with those at non‐RLC sites. Estimating the crash vulnerability from not‐at‐fault crash involvements, the study shows that with a RLC, the relative crash vulnerability (RCV) or crash‐involved exposure of motorcycles at right‐angle crashes is reduced. Furthermore, field investigation of motorcycle maneuvers reveal that at non‐RLC arms, motorcyclists usually queue beyond the stop line, facilitating an earlier discharge, and hence become more exposed to the conflicting stream. However at arms with a RLC, motorcyclists are more restrained to avoid activating the RLC and hence become less exposed to conflicting traffic during the initial period of the green. The study also shows that in right‐angle collisions, the proneness of at‐fault crashes of motorcycles is lowest among all vehicle types. Hence motorcycles are more likely to be victims than the responsible parties in right‐angle crashes. RLCs have also been found to be very effective in reducing at‐fault crash involvements of other vehicle types which may implicate exposed motorcycles in the conflicting stream. Taking all these into account, the presence of RLCs should significantly reduce the vulnerability of motorcycles at signalized intersections. Copyright © 2010 John Wiley & Sons, Ltd.