Energy use in cities has attracted significant research in recent years. However such a broad topic inevitably results in number of alternative interpretations of the problem domain and the modelling tools used in its study. This paper seeks to pull together these strands by proposing a theoretical definition of an urban energy system model and then evaluating the state of current practice. Drawing on a review of 219 papers, five key areas of practice were identified -technology design, building design, urban climate, systems design, and policy assessment -each with distinct and incomplete interpretations of the problem domain. We also highlight a sixth field, land use and transportation modelling, which has direct relevance to the use of energy in cities but has been somewhat overlooked by the literature to date.Despite their diversity, these approaches to urban energy system modelling share four common challenges in understanding model complexity, data quality and uncertainty, model integration, and policy relevance. We then examine the opportunities for improving current practice in urban energy systems * Corresponding author Email addresses: j.keirstead@imperial.ac.uk (James Keirstead), m.jennings09@imperial.ac.uk (Mark Jennings), a.sivakumar@imperial.ac.uk (Aruna Sivakumar) Preprint submitted to Renewable and Sustainable Energy ReviewsOctober 5, 2011modelling, focusing on the potential of sensitivity analysis and cloud computing, data collection and integration techniques, and the use of activity-based modelling as an integrating framework. The results indicate that there is significant potential for urban energy systems modelling to move beyond single disciplinary approaches towards a sophisticated integrated perspective that more fully captures the theoretical intricacy of urban energy systems.

The Comprehensive Econometric Micro-simulator for Daily Activity-travel Patterns (CEMDAP) is a micro-simulation implementation of an activity-travel modeling system. Given as input various land-use, sociodemographic, activity system, and transportation level-of-service attributes, the system provides as output the complete daily activity-travel patterns for each individual in each household of a population. This paper describes the underlying econometric modeling framework and the software development experience associated with CEMDAP. The steps involved in applying CEMDAP to predict activity-travel patterns and to perform policy analysis are also presented. Empirical results obtained from applying the software to the Dallas/Fort-Worth area demonstrate that CEMDAP provides a means of analyzing policy impacts in ways that are generally infeasible with the conventional four-stage approach.Bhat, Guo, Srinivasan and Sivakumar 1 INTRODUCTIONThe activity-based approach to travel demand analysis views travel as a demand derived from the need to pursue activities distributed in space (1,2). The approach adopts a holistic framework that recognizes the complex interactions in activity and travel behavior. The conceptual appeal of this approach originates from the realization that the need and desire to participate in activities is more basic than the travel that some of these participations may entail. Due to the emphasis on activity behavior patterns, such an approach can address congestion-management issues through an examination of how people modify their activity participations (for example, will individuals substitute more out-of-home activities for in-home activities in the evening if they arrived early from work due to a work-schedule change?).Activity-based travel analysis has seen considerable progress in the past couple of decades and has led to the development of several comprehensive activity-travel models. These models typically fall into one of two categories: econometric models and computational process models. The econometric modeling approach involves using systems of equations to capture relationships among activity and travel attributes, and to predict the probability of decision outcomes. The strength of this approach lies in allowing the examination of alternative hypotheses regarding the causal relationships between activity-travel patterns, land use and socio-demographic characteristics of individuals. A computational process model is, on the other hand, a computer program implementation of a production system model, which is a set of rules in the form of condition-action (IF-THEN) pairs that specify how a task is solved (3). The approach focuses on the process of decision-making and captures schedule constraints explicitly. Hence, the computational process models potentially offer more flexibility than econometric models in representing the complexity of travel decision-making.The desire to move activity-travel models -both the econometric models and the computational process models -into o...

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The promotion of space sharing in order to raise the quality of community living and safety of street surroundings is increasingly accepted feature of modern urban design. In this context, the development of a shared space simulation tool is essential in helping determine whether particular shared space schemes are suitable alternatives to traditional street layouts. A simulation tool that enables urban designers to visualise pedestrians and cars trajectories, extract flow and density relation in a new shared space design, achieve solutions for optimal design features before implementation, and help getting the design closer to the system optimal. This paper presents a three-layered microscopic mathematical model which is capable of representing the behaviour of pedestrians and vehicles in shared space layouts and it is implemented in a traffic simulation tool. The top layer calculates route maps based on static obstacles in the environment. It plans the shortest path towards agents' respective destinations by generating one or more intermediate targets. In the second layer, the Social Force Model (SFM) is modified and extended for mixed traffic to produce feasible trajectories. Since car movements are not as flexible as pedestrian movements, velocity angle constraints are included for cars. The conflicts described in the third layer are resolved by rule-based constraints for shared space users. An optimisation algorithm is applied to determine the interaction parameters of the force-based model for shared space users using empirical data. This new three-layer microscopic model can be used to simulate shared space environments and assess, for example, new street designs.