Influence of rainfall on quality of service at multilane roundabouts and its time headway implications.

Doctor of Philosophy in Civil Engineering. University of KwaZulu-Natal. Durban, 2018.Roundabouts, or traffic circles as they are often called in South Africa, are priority intersections with a unique yield rule. Drivers approaching the roundabout must give way to those that are already circulating the central island. The fixed features and yield rule do not change relative to rainfall; however, vehicular flow rate and driver behaviour are often affected by ambient conditions like rainfall among others. Consequently, in this the study the influence of rainfall on the quality of service delivery at multilane roundabouts and their implications for time headways have been investigated. Based on the hypothesis that rainfall, irrespective of intensity, has adverse effects on the quality of service delivery and time headway at roundabouts, an impact study was carried out in Durban, South Africa. Entry, circulating traffic flow rate and rainfall data were collected at four selected sites in Durban, South Africa. Over one million traffic volume data was collected during the August 2016 to February 2017 rainy season. The key selection criterion is proximity to an active rain gauge. Empirical data were collected continuously for six weeks on each selected roundabout. Rainfall data were collected from surface rain gauge stations with a distance range of 0.75km – 1.18km from the selected sites. Three classes of rain precipitation intensity (i) (light rain, i < 2.5mm; moderate rain, 2.5mm < i ≤10mm; and heavy rain 10mm < i ≤ 50mm) were considered. Very heavy rain, with an intensity greater than 50mm/h, was not considered because of associated drag force and aquaplaning which might be difficult to separate from the rainfall effect. Daylight data were separated into peak and off-peak traffic periods. Peak period data were used to develop a quality of service criteria table and the off-peak data were used to determine traffic flow rate performance. Passenger car equivalent (PCE) values used to convert vehicles per hour to pce per hour was investigated for analytical suitability given rainy conditions. Entry flow rate was used as a function of circulating flow rate to model entry capacity and, hence, determine the reserve capacity. Initially, both linear and exponential models were used, in turn, to test for analytical suitability. Linear model was the preferred after exponential function failed empirical tests. Linear function was used to model the relationships between entry and circulating traffic flow rates. The ensuing entry capacity was also used in conjunction with headway and degree of saturation to estimate entry delay under dry, light, moderate and heavy rainy conditions. The impact study reasons that quality of service is not the same as level of service, hence, the criteria table cannot be the same. This is a clear departure from Highway Capacity Manual (HCM) prescription for roundabout level of service criteria table. The novel quality of service criteria table prescribed in this thesis, has delay and reserve capacity as the xxxi key determinants of service grade. It is also referred to as Functional Quality of service (FQS) in the thesis. FQS criteria table was developed for each study site and used to assess their service delivery. The criteria table was divided into six classes (A to F), where A is the best grade and F is the worst. In any case, traffic performances were analysed and results show that; i) there is no significant difference between South Africa passenger car equivalent values and those estimated in the study; ii) the novel criteria table developed in the study is an effective determinant of FQS delivery at roundabouts; iii) entry traffic flow rate rates decreased because of rainfall and by extension induced a reduction in quality of service delivery at all surveyed sites; iv) entry delay and attendant queue increased during rainfall; v) time headway increased and entry reserve capacity decreased because of rainfall. It has been concluded that rainfall has an adverse effect on the FQS and also, that heavy rainfall has the most significant impact on FQS at roundabouts. It is proposed that in future research, on roundabout entry capacity estimation based on polynomial quadratic function where the single-variable quadratic polynomial would have density as the independent variable and flow rate as the dependent be considered

Information and decentralization in inventory, supply chain, and transportation systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2006.Includes bibliographical references (p. 199-213).This thesis investigates the impact of lack of information and decentralization of decision-making on the performance of inventory, supply chain, and transportation systems. In the first part of the thesis, we study two extensions of a classic single-item, single-period inventory control problem: the "newsvendor problem." We first analyze the newsvendor problem when the demand distribution is only partially specified by some moments and shape parameters. We determine order quantities that are robust, in the sense that they minimize the newsvendor's maximum regret about not acting optimally, and we compute the maximum value of additional information. The minimax regret approach is scalable to solve large practical problems, such as those arising in network revenue management, since it combines an efficient solution procedure with very modest data requirements. We then analyze the newsvendor problem when the inventory decision-making is decentralized. In supply chains, inventory decisions often result from complex negotiations among supply partners and might therefore lead to a loss of efficiency (in terms of profit loss).(cont.) We quantify the loss of efficiency of decentralized supply chains that use price-only contracts under the following configurations: series, assembly, competitive procurement, and competitive distribution. In the second part of the thesis, we characterize the dynamic nature of traffic equilibria in a transportation network. Using the theory of kinematic waves, we derive an analytical model for traffic delays capturing the first-order traffic dynamics and the impact of shock waves. We then incorporate the travel-time model within a dynamic user equilibrium setting and illustrate how the model applies to solve a large network assignment problem.by Guillaume Roels.Ph.D

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen

Catalog, University of Missouri--Columbia, undergraduate (January 1985)

"January 1985