A Model of the Rise and Fall of Roads

Transportation network planning decisions made at one point of time can have profound impacts in the future. However, transportation networks are usually assumed tobe static in models of land use. A better understanding of the natural growth pattern of roads will provide valuable guidance to planners who try to shape the future network. This paper analyzes the relationships between network supply and travel demand, and describes a road development and degeneration mechanism microscopically at the linklevel. A simulation model of transportation network dynamics is developed, involving iterative evolution of travel demand patterns, network revenue policies, cost estimation,and investment rules. The model is applied to a real-world congesting network – the Twin Cities transportation network which comprises nearly 8,000 nodes and more than 20,000 links, using network data collected since year 1978. Four experiments are carried out with different initial conditions and constraints, the results from which allow us toexplore model properties such as computational feasibility, qualitative implications, potential calibration procedures, and predictive value. The hypothesis that roadhierarchies are emergent properties of transportation networks is confirmed, and the underlying reasons discovered. Spatial distribution of capacity, traffic flow, andcongestion in the transportation network is tracked over time. Potential improvements to the model in particular and future research directions in transportation network dynamicsin general are also discussed.Transportation network dynamics, Urban planning, Road suppl

From Social Simulation to Integrative System Design

As the recent financial crisis showed, today there is a strong need to gain "ecological perspective" of all relevant interactions in socio-economic-techno-environmental systems. For this, we suggested to set-up a network of Centers for integrative systems design, which shall be able to run all potentially relevant scenarios, identify causality chains, explore feedback and cascading effects for a number of model variants, and determine the reliability of their implications (given the validity of the underlying models). They will be able to detect possible negative side effect of policy decisions, before they occur. The Centers belonging to this network of Integrative Systems Design Centers would be focused on a particular field, but they would be part of an attempt to eventually cover all relevant areas of society and economy and integrate them within a "Living Earth Simulator". The results of all research activities of such Centers would be turned into informative input for political Decision Arenas. For example, Crisis Observatories (for financial instabilities, shortages of resources, environmental change, conflict, spreading of diseases, etc.) would be connected with such Decision Arenas for the purpose of visualization, in order to make complex interdependencies understandable to scientists, decision-makers, and the general public.Comment: 34 pages, Visioneer White Paper, see http://www.visioneer.ethz.c

Shawn: A new approach to simulating wireless sensor networks

We consider the simulation of wireless sensor networks (WSN) using a new approach. We present Shawn, an open-source discrete-event simulator that has considerable differences to all other existing simulators. Shawn is very powerful in simulating large scale networks with an abstract point of view. It is, to the best of our knowledge, the first simulator to support generic high-level algorithms as well as distributed protocols on exactly the same underlying networks.Comment: 10 pages, 2 figures, 2 tables, Latex, to appear in Design, Analysis, and Simulation of Distributed Systems 200

Systematic Analysis of Rebound Effects for "Greening by ICT" Initiatives

The application of ICT can lead to considerable reductions in the energy consumption of society. Although ICT itself consumes energy, there are many good reasons to explore the possibilities of 'green ICT'. After decades of experiments and research, ICTs designed to be 'green' still holds the promise of leading to substantial ecological benefits by means of dematerialisation, more efficient production processes and changed (more sustainable) human behaviour. Up till now, the effects of ICT on energy consumption are much less straightforward due to rebound effects: effects that have a negative influence on the intended positive effect. In parallel, rebound effects themselves have in turn other side effects as well, so there are many interacting effects to account for, greatly adding to complexity of the discussion. Despite evidence that suggests otherwise, initiatives that focus on 'greening by ICT' do notaccount for a consistent analysis of these rebound effects. This paper proposes an approach that enables to map and analyze these rebound effects systematically. This approach is applied in two related cases, teleworking and the use of Smart Working Centres. The Rapid Assessment Program (RAP) is used as a simulation model to identify which chains of effects are most interesting to consider for intervention. The application in the two cases demonstrates that rebound effects can by structured and that the RAP is a very suitable way to do so and provides a good assessment of net sustainability effects.rebound effects, Rapid Assesment Program, greening by ICT, teleworking.