Structural phase transitions in multipole traps

A small number of laser-cooled ions trapped in a linear radiofrequency multipole trap forms a hollow tube structure. We have studied, by means of molecular dynamics simulations, the structural transition from a double ring to a single ring of ions. We show that the single-ring configuration has the advantage to inhibit the thermal transfer from the rf-excited radial components of the motion to the axial component, allowing to reach the Doppler limit temperature along the direction of the trap axis. Once cooled in this particular configuration, the ions experience an angular dependency of the confinement if the local adiabaticity parameter exceeds the empirical limit. Bunching of the ion structures can then be observed and an analytic expression is proposed to take into account for this behaviour

Road Incidents and Network Dynamics: Effects on driving behaviour and traffic congestion

Incidents cause a large part of the congestion on the road. This PhD study describes how people change their behaviour when facing an incident situation. It is found that car-following behaviour changes and drivers react slower on their predecessors. Furthermore, it is found that drivers change their route when facing unexpected delay caused by an incident. The route choice if the queue is caused by an incident is different from the situation with a similar queue which is not caused by an incident. Also the queuing patterns in the network are studied. It is found that so called “spillback” effects are important. This is a queue with cars heading to a direction with a bottleneck which blocks the cars to another direction, which do not need to pass the bottleneck. Due to these effects, it is essential to use an accurate representation of traffic when calculating the total delays of an incident. The findings of this thesis can be used for creating more robust road networks, causing less delay in case of incidents.Transport & PlanningCivil Engineering and Geoscience

Introduction to Traffic Flow Theory: An introduction with exercises

Traffic processes cause several problems in the world. Traffic delay, pollution are some of it. They can be solved with the right road design or traffic management (control) measure. Before implementing these designs of measures, though, their effect could be tested. To this end, knowledge of traffic flow theory is needed.This book is meant as learning book for students. To learn an engineering discipline, practicing is essential. One of the core qualities of this book, is that more than 250 practice questions (and answers) are available. Therefore, this book can be used as material for courses.Transport and Plannin

Traffic Flow Theory: An introduction with exercises

Traffic processes cause several problems in the world. Traffic delay, pollution are some of it. They can be solved with the right road design or traffic management (control) measure. Before implementing these designs of measures, though, their effect could be tested. To this end, knowledge of traffic flow theory is needed.Transport and Plannin

Automatic fitting procedure for the fundamental diagram

The fundamental diagram of a road, including free-flow capacity and queue discharge rate, is very important for traffic engineering purposes. In the real word, most traffic measurements come from stationary loop detectors. This paper proposes a method to fit Wu's fundamental diagram to loop detector data. Wu's fundamental diagram is characterised by five parameters, being free-flow speed, wave speed, free-flow capacity, queue discharge rate and jam density. The proposed method entails fixing the wave speed and the free-flow speed. The method consists of two steps. We first use a triangular fundamental diagram to separate the congested branch from the free-flow branch. Then, the remaining three parameters of Wu's fundamental diagram are fitted on each branch using a least-square fit. This method is shown to be robust for cases tested in real life, and hence very noisy, data

The effect of crosswalks on traffic flow

In urban areas and especially in inner cities, pedestrians crossing the road considerably influence the road traffic flow. For political reasons, priority could be given to pedestrians. A larger number of crossings reduces the pedestrian load per crossing and facilitates both the pedestrian flow and the car flow; the ultimate case is a “cross anywhere” scenario. Earlier work shows that the road capacity decreases with the square of the pedestrian crossing time, hence a short crossing time is desired. Crosswalks can ensure pedestrians cross orthogonally, and thus quickly, and can thereby improve traffic flow. Moreover, a limited number of crosswalks is less stressful than a “cross any-where” scenario for a car driver since (s)he only needs to expect crossing pedestrians at dedicated crosswalks. This paper studies the effect of the distances between crosswalk and road traffic capacity. The paper’s goal is finding a single formula or universal set of charts that can describe the effect of pedestrian crosswalks on traffic flow under virtually all scenarios (with long blocks). This type of result would obviate the need for simulations of specific situations when only a rough assessment of the effect of crosswalks is desired. Traffic flow for several distances between pedestrian crossings is simulated, and moreover, a non-constant inter-crosswalk spacing is considered. The simulation results can be used for other situations, using transformations and an interpolation recipe. Overall, the closer the crosswalks, the better the flow. However, spacings closer than approximately 25-50 meters do not add much. Speed of traffic under a broad array of pedestrian crossing scenarios is given.</p

The Value of Calibration and Validation of Probabilistic Discretionary Lane-Change Models (poster)

This paper analyses methodologies to calibrate and validate probabilistic lane change models. We perform a calibration and validation on lane change models (microscopic and macroscopic) which take the most basic dependencies into account. The resulting model has reasonable parameters, and the goodness of fit for the validation set (hold back from the total set) is similar to the calibration. For two measures of validation the model hence is validated. However, in real world terms, the model performs quite bad. It is hence concluded that the model should be validated based on measures which have a clear physical interpretation, and based on those the quality should be judged.Transport and PlanningCivil Engineering and Geoscience