MSc projects

Speed limits and their effect on freeway capacity

By: William van Lindonk

In this thesis an investigation is performed into the effect of different speed limits on freeway capacity. From literature, much is known about the variety of factors that affect capacity, but the exact effect of the speed limit on capacity is not yet clear. In recent years, several speed limits changes have taken place at multiple two-lane freeway bottlenecks throughout The Netherlands, which makes it possible to compare effects of different speed limits at the same location. To evaluate the effect of the speed limit on capacity, the Product Limit Method has been applied to identify breakdown flows and generate capacity distributions, which could subsequently be compared for different limits. In the comparison of capacity distributions under different speed limits, it was found that significant changes in capacity had occurred, but that no uniform direction of the effect could be found. Subsequently, to control for location specific factors and other variables, Fixed Effects regression has been used to determine the effect of the speed limit on the breakdown flow. It was found that the breakdown flow under the 120 km/h limit was significantly higher than under the 130 km/h limit (in the range of 60 to 190 vehicles per hour) and that the breakdown flow under the 100 km/h limit was, in some cases, also higher than under the 130 km/h limit. In addition to this, it was found that a significant positive relation exists between the height of the speed limit and the fraction of flow in the passing lane. Moreover, it was shown that the relation between the fraction of flow in the passing lane and the level of breakdown flow was best represented by a quadratic relation, which could indicate that an “optimal” distribution of flows may exist. Given the results of this thesis, it is posed that a change in the speed limit is likely to affect capacity primarily through altering the lane flow distribution and that it will depend on the layout of a freeway location what the optimal lane flow distribution is and which speed limit leads to this optimal lane flow distribution.

Representing the Car-Following Behaviour of Adaptive Cruise Control (ACC) Systems Using Parametric Car-Following Models

By: Mathieu Blauw

The goal of this research was to gain insights into the performance of commonly applied parametric car-following models on representing the driving behaviour of ACC systems. Optimal model calibration was obtained by investigating the sensitivity of the model calibration to synthetic data. Investigated were the calibration methodology and the quality and quantity of calibration data. Models are calibrated to real-world driving data from an Audi A4 from 2017. For the ACC system, it was found: 1)the ACC system exhibits non-linear driving behaviour, 2)the acceleration depends on the current velocity and distance to the desired velocity, 3)the system does not consider an intelligent braking strategy and is thus not able of handling safety-critical driving situations and 4)the model includes a sub-controller which ensures comfortabledriving behaviour.

Modelling traffic in the Randstad using a dynamic zone model based on the Network Fundamental Diagram

By: Mark Sloot

This master thesis focusses on the usability of a dynamic zone-based traffic assignment model for large areas,using the concept of the Network Fundamental diagram. These kinds of models differ from the traditional traffic assignment models, because the conventional models are suitable for modelling traffic networks consisting of links, rather than zone.  The simulation model that is used in this case study for the Randstad is a newly developed model in-spired by the Network Transmission Model. The main difference lies in the way the demand to the neighboring zone is constructed.

The model then works as follows. For each observed density on the freeway network the corresponding densities on the lower-hierarchy roads are calculated, as well as the weighted average density forthe full network. With these densities and the fundamental diagrams, the weighted average network flow is calculated. The resulting weighted average densities and flows are then plotted in theK,P-diagram and a multi-linear line is fitted through the points. With this input, the simulation can be performed. Generally, the model is able to reproduce the shapes of the outflow patterns, taking into account the de-sired range of 20%, but some zones show large deviations. Especially for the zones Den Haag and Rotterdam the outflow is particularly during morning peak much higher than the observed value.

New Intersection Control for Conventional and Automated Vehicles without Traffic Lights

A combination of self-regulation and individual control

By: Anna Cristofoli

Typically, an intersection consists of a number of approaching roads and a crossing area. This thesis aims to develop a novel control strategy that efficiently controls traffic withdifferent penetration rates by relying purely on wireless communication to integrate the control of automated and human drivers. Automated vehicles are considered to be also connected while conventional vehicles are not. The intersection does not need traffic lights sowhile V2I communications can be used to individually control automated vehicle, the motion of conventional vehicles will be indirectly influenced by controlling the speed of automated vehicles. From a design perspective, the solution framework is translated into a bi-level optimization problem with the ultimate goal of computing the acceleration profile (control signal) of controlled “i-platoons” (i.e., platoons lead by a controlled vehicle, possibly followed by  non controlled vehicles) that yields the minimal total delay for all i-platoons in the network. The upper level optimization is a combinatorial optimization that aims to find the sequence of i-platoons with the least delay. In the upper level, each sequence is associated with a control signal which generate the least delay for that sequence. This optimization is solved in the lower level, where, given that sequence, the best acceleration profile is computed. he results show that the traffic control strategy is able to improve the efficiency of the intersection under unsaturated conditions . This results is achieved already with low penetration rate of 20%. During saturated conditions,the control strategy shows a performance drop. When uncontrolled i-platoons start queuing on the minor road and there is not enough platoons on the major road to slow down in favor of theminor road, the traffic condition cannot be improved.