The effect of green time on stochastic queues at traffic signals

Many analyses of traffic signal queues use Webster and Cobbe's formula, which combines the net effect of the red/green cycle with a term representing stochastic effects, idealised as an M/D/1 queue process having random arrivals and uniform service. Several authors have noted that this component should depend not only on demand intensity but also on throughput capacity in each green period, although an extra empirical term may partially allow for this. Extending the service interval in M/D/1 (M = Markovian, i.e. random, D = deterministic, i.e. uniform, 1 = one server) enables the effect to be reproduced, but no exact expressions for its moments are found. Approximate formulae for the extended mean exist but are accurate only near saturation. The paper derives novel approximations for the equilibrium mean and also variance and utilisation, using functions linking traffic intensity with green period capacity. With three moments, equilibrium probability distributions can be estimated for which a method based on a doubly nested geometric distribution is described.     

拥挤收费的政治策略

通过收费缓解交通拥堵的政治可行性取决于谁获得通行费收入。指出如果收益被分配给城市,特别是高速公路经过的城市,拥挤收费取得政治成功的可能性最大。与已有的很多建议不同,指出城市是比个体驾驶人和区域政府更有力的收益申索人。基于行为经济学和政治科学理论并结合几个大都市区的数据,对提议进行解析和阐述。在洛杉矶,潜在的拥挤收费收入估计每年接近50亿美元,将这些收入分配至高速公路经过的城市对拥挤收费的实施是有政治影响力和促进作用的。     

Linking ocean container carrier capabilities to shipper–carrier relationships: a case study

ABSTRACT

As outsourcing and offshoring continue to expand, the ocean container industry serves a critical and still increasing role in supporting global trade. Yet, perceived commoditization and intense price competition among ocean container carriers limit opportunities for competitive advantage and formation of long-term shipper–carrier relationships. This environment ultimately yields an unhealthy industry that threatens the stability of global supply chains. Extant literature provides limited insight into how carriers can build strong relationships with shippers to overcome the short-term, transactional-orientation of the industry. Examining a case study of a major ocean container carrier, we apply structural equation modeling to shipper survey data to explore how carrier operational, service, and pricing capabilities influence the strength of the long-term shipper–carrier relationship. Furthermore, we identify unique clusters of shipper needs, helping the carrier understand when and how to promote a particular portfolio of capabilities to customers.     

Mature hub ports in the free trade environment,the way forward from a global supply chain perspective: an Asian case

Asia-Pacific countries with divergent economic and political backgrounds developed a regime of bilateral free trade agreements in response to globalization. Challenged by the 1997 and 2008 financial crises, this Asian trade regime has remained intact, although the most powerful stakeholders have changed positions, as indicated by the strong emergence of China in the past decade. Efforts of key trading partners to tackle non-tariff barriers (e.g., rule of origin and customs formalities) in the region have yielded little progress thus far. Instead of aiming at a regional consensus on non-tariff barriers by all member states, a global supply chain (GSC) approach is recommended. Mature hub ports at strategic locations with advanced institutional measures could set up international trade facilitation centers co-locating multinational customs formalities. This GSC approach may also be adopted to construct a GSC hub development model that explains the transformation of hub ports.     

Towards a meta-analysis and toolkit for port-related socio-economic impacts: a review of socio-economic impact studies conducted for seaports

Port authorities increasingly need to communicate with a variety of external stakeholders in order to maintain and strengthen the societal acceptance of seaport activities. The availability of socio-economic impact studies on port authority and regional development agency websites has often made this information accessible to the public at large. However, the differences in methodologies adopted, in terms of selecting, defining and measuring various types of socio-economic impacts, sometimes lead to misconceptions as well as misleading comparisons across ports within and between regions. In this paper, we suggest guidelines for the design and application of a potential best practice from an interregional perspective (UK, France and Belgium), based on research in the framework of a European Commission co-funded project, ‘IMPACTE’. The paper also aims to develop guidelines for comparing the socio-economic impacts of ports across regional and national borders and discusses the development of a European port economic impact measurement toolkit. We analyse a sample of 33 recent socio-economic impact assessment reports in terms of methodologies adopted and types of impacts measured. The review shows a great diversity among these studies, leading to important differences between the impacts of port activity communicated to stakeholders.     

The biogeochemical cycling of methane in Ria de Vigo, NW Spain: Sediment processing and sea–air exchange

Methane (CH₄) concentrations were measured in the water column, in sediment porewaters, and in atmospheric air, in the Ría de Vigo, NW Spain, during both the onset (April 2003) and at the end of (September 2004) seasonal upwelling. In addition, CH₄ concentration and stable isotopic signatures (δ¹³CH₄) were measured in porewaters, and sediment methanogenesis and aerobic oxidation of CH₄ were determined in sediment incubations. Surface water column CH₄ (2 m depth) was in the range 3–180 nmol l^− 1 (110–8500% saturation) and followed a generally landward increase but with localised maxima in both the inner and middle Ría. These maxima were consistent with CH₄ inputs from underlying porewaters in which CH₄ concentrations were up to 3 orders of magnitude higher (maximum 350 μmol l^− 1). Surface water CH₄ concentrations were approximately three times higher in September than in April, consistent with a significant benthic CH₄ flux driven by enhanced sediment methanogenesis following the summer productivity maximum. CH₄ and δ¹³CH₄ in sediment porewaters and in incubated sediment slurries (20 °C) revealed significant sediment CH₄ oxidation, with an apparent isotopic fractionation factor (r_c) of  1.004. Using turbulent diffusion models of air–sea exchange we estimate an annual emission of atmospheric CH₄ from the Ría de Vigo of 18–44 × 10⁶ g (1.1–2.7 × 10⁶ mol). This estimate is approximately 1–2 orders of magnitude lower than a previous estimate based on a bubble transport model.     

A conflict model and interactive simulator (FASTCARS) for predicting enroute driver behavior in response to real-time traffic condition information

This paper proposes a theoretical methodology and practical data collection approach for modeling enroute driver behavioral choice under Advanced Traveler Information Systems (ATIS). The theoretical framework is based on conflict assessment and resolution theories popularized in psychology and applied to models of individual consumer behavior. It is posed that enroute assessment and adjustment is a reactionary process influenced by increased conflict arousal and motivation to change. When conflict rises to a level at which conflict exceeds a personal threshold of tolerance, drivers are likely to alter enroute behavior to alleviate conflict through either route diversion of goal revision. Assessment and response to conflict arousal directly relate to the driver's abilities to perceive and predict network conditions in conjunction with familiarity of network configurations and accessible alternate routes.Data collection is accomplished through FASTCARS (Freeway andArterialStreetTrafficConflictArousal andResolutionSimulator), in interactive microcomputer-based driving simulator. Limited real-world implementation of ATIS has made it difficult to study or predict individual driver reaction to these technologies. It is contended here that in-laboratory experimentation with interactive route choice simulators can substitute for the lack of real-world applications and provide an alternate approach to data collection and driver behavior analysis. This paper will explain how FASTCARS is useful for collecting data and testing theories of driver behavior.     

Transport policy in Eastern Europe a case study of Hungary

This paper analyses the development of transport policy making in Eastern Europe over the last forty years and describes the role of the CMEA in determining national developments in Poland, Romania, East Germany, Czechoslovakia, Hungary and Bulgaria. The USSR, Albania and Yugoslavia are excluded. The planning system as operated in the Eastern Block, is described, followed by a particular case study of Hungarian policy making with respect to the transport sector. Specific tansport issues relating to Hungary are outlined before conclusions are drawn in terms of future developments in relation with the European Community.     

Forecasting tanker freight rate using neural networks

Improvement in forecasting accuracy is a difficult task but critical for business success. This paper investigates the potential of neural networks for short- to long-term prediction of monthly tanker freight rates. Procedures are outlined for the development of the neural networks. The problem of under-training and over-training is addressed by controlling the number of iterations during the training process of neural networks. A comparative study of predictive performance between neural networks and ARMA time series models is conducted. Our evience shows that neural networks can significantly outperform time series models, especially for longer-term forecasting.