Ramon L. Landman

Policy-Based, Service Level-Oriented Route Guidance in Road Networks

The realization of traffic management on a network level is not only theoretically complex, but also practically challenging because the traffic management policy of the road authorities must be taken into account. In the Netherlands, this policy harmonizes the interests of involved stakeholders by means of a common vision on the functioning of the network, expressed in road priorities and the corresponding target service levels. As a result, network states that reflect the policys objectives in a systematic and comprehensible way must be realized. This paper presents a predictive route guidance approach that is able to operationalize the formulated policy. This approach degrades and restores target service levels of routes according to their difference in priority, with respect to the network performance. The control approach consists of a finite state machine that determines target service levels according to predicted traffic conditions. These target service levels are used as setpoints in a feedback controller, and the result is a corresponding output signal of a variable message sign. By means of a test case, the finite state machine is compared with a model predictive route guidance controller (that realizes system optimal conditions) and with a user equilibrium feedback controller (that realizes user optimal conditions). Results showed that the finite state machine was able to prevent or limit the effects of phenomena that caused decreased network performance in a comprehensible and efficient way while also accounting for the interests of the road users.

Vehicle-class Specific Route-guidance of Freeway Traffic by Model-predictive Control

Few active traffic management measures proposed in the past considered the distinction of different vehicle classes. Examples of measures specific to vehicle class are truck lanes and high-occupancy toll lanes. It is proposed that the distinction of different vehicle classes, with different flow characteristics and societal and economic functions, can contribute to the effectiveness of traffic management measures. This study developed a multiclass controller that rerouted the traffic class specifically. Vehicle class–specific properties such as vehicle length and value of time were used in a model-predictive control approach to minimize the total time spent in the network by vehicles and the corresponding economic costs. By means of a simple test case with synthetic data, it was shown that a multiclass controller outperformed a single-class controller and that the multiclass control signals were sensitive to the value of time and the capacity of the network.

Integrated Network Management Amsterdam: Control approach and test results

The Praktijkproef Amsterdam (Field Operational Test Integrated Network Management Amsterdam) is one of the first large-scale FoTs testing coordinated network wide deployment of traffic management in practice. After a successful Proof-of-Concept (PoC) in 2009, in 2013 the first parts of the concept approach will be tested in the field, working towards a full deployment from 2014 onwards. This paper describes the hierarchal control approach that has been developed in order to operationalise the control paradigm developed during the PoC. The paper explains this control framework, the functional architecture, and the main control algorithms. The paper also shows the first results of the application of the control approach in a simple test network.

Design and Implementation of Integrated Network Management Methodology in a Regional Network

Praktijkproef Amsterdam (Field Operational Test Integrated Network Management Amsterdam) is a project focused on the design and implementation of an innovative system for the coordinated deployment of traffic management measures in the regional network around the city of Amsterdam, Netherlands. On the basis of the generic functional architecture described in previous publications, monitoring and control functions were specified, implemented, tested, and tuned, both in a model environment and in practice. The focus here is on the controller design, which adapts and generalizes the master–slave structure used in the well-known HERO algorithm. It is shown how the principles are applied to use the urban arterials as storage locations for freeway metered traffic as well as to solve problems occurring on the urban arterials themselves—for example, in the case of spillback or gridlock. The key control principles are explained and the resulting feedback controller is analyzed to show how to choose its parameters to ensure stability and minimize the time needed to achieve the target value. To this end, a new methodology is proposed to analyze the dynamics of the controller in relation to the control parameters for different controller designs. Finally, the implementation of the system is discussed, and preliminary tuning and evaluation results from the field tests are provided.

Coordinated Ramp Metering Based on On-Ramp Saturation Time Synchronization

In this paper, a coordinated ramp-metering approach is proposed; the approach is based on the synchronization of the time it takes for an on-ramp to run out of space. The time that congestion and the associated capacity drop can be prevented at a freeway bottleneck by means of ramp metering depends on the available ramp space for temporarily storing the vehicles. For a single on-ramp, the available space and thus the metering time at the bottleneck are often limited. By means of coordination, upstream storage space can be used to prevent a breakdown for a longer period of time. To accomplish that aim, upstream ramps need to reduce their inflow into the mainstream with respect to their own metering task. The extent to which upstream inflow reductions are effectively used to extend the metering time at the bottleneck is determined by the order and timing at which the coordinated ramps run out of space. The proposed approach aims at always saturating the more upstream-located ramps before more downstream-located ones; that is, the ramps run out of space in the downstream direction to make sure that all realized assistance is used by the ramp that is metering at the bottleneck. By means of a simulation test case, the functioning of the algorithm is demonstrated and compared with a no-control scenario, local ramp metering, and an alternative coordination algorithm that aims at filling the ramps equally. Both coordination approaches strongly improve the network performance with respect to local ramp metering, but the proposed coordination approach is able to postpone the breakdown for a longer period of time.

Service level-oriented route guidance for overlapping routes in road networks: A comparison with MPC

Service level control is a promising strategy to operationalize policy objectives within road networks. In previous work we have introduced a route guidance approach that controls service levels over two alternative routes. However, when applying the method on a network level with multiple actuators, controlled routes might overlap. Interaction between the controllers then occurs, because the traffic that flows towards overlapping route stretches can be manipulated from multiple directions. In this contribution the interaction mechanism is described and verified by means of a simulation test case. The functioning of the proposed method is compared with a model predictive route guidance controller that realizes optimal conditions given the prevailing policy objectives. Results show that the interaction mechanism successfully prevents network performance degradation by directing traffic such that available capacity over route alternatives is fully utilized. If target service levels are properly defined, queue spill back towards upstream infrastructure is delayed or even prevented. With respect to equity, the performance difference over the routes is limited by degrading and recovering the target service levels of the controlled routes stepwise. To conclude, the approach can be tuned such that optimal performance is approximated, but with a significantly lower computational demand and a better scalability with growing network sizes.

Urban Storage Space Selection Method for Integrated Control on a Freeway Bottleneck

Ramp metering is an effective means to reduce freeway bottleneck delay that results from the capacity drop phenomenon when congestion sets in. The bottleneck flow is kept at free-flow capacity by temporarily storing vehicles traveling toward the bottleneck at the ramp. The metering duration is normally limited because of the finite amount of ramp storage space available to prevent undesired spill back to the urban network. A beneficial extension of the metering duration might be achieved by strategically choosing upstream intersection arms that reduce their inflow to the ramp. For that purpose, coordination needs to be realized between the ramp meter and its intersection controllers located upstream, which will also hinder vehicles not traveling toward the ramp. In this contribution, an evaluation approach is put forward to decide objectively which intersection buffers (arms) should be included in the coordination. To quantify the resulting delays in the system, cumulative inflow and outflow curves are developed as a function of the involved situation-specific variables. This approach enables one to determine the optimal set of coordinated buffers beforehand and to gain insight into the effect of the various system variables on the delays. By means of worked examples, these effects are illustrated, and the way to determine the optimal set of coordinated buffers is shown. Results show that the length of the peak period and the size of the capacity drop strongly determine the coordination benefits, and, hence, a buffer’s minimum required fraction of traffic traveling past the bottleneck needed to result in beneficial coordination.

On-ramp Selection Methodology for Coordinated Ramp Metering Schemes

Coordinated ramp metering is an effective means to reduce freeway bottleneck delay by postponing the moment of a flow breakdown and the associated capacity drop. To this aim, vehicles are stored at upstream located ramps to reduce the flow towards the bottleneck, causing delays at the ramps to both vehicles that move towards the bottleneck and to those that leave the network elsewhere. There are several different network characteristics that determine the resulting total ramp and bottleneck delays, and hence, whether it is beneficial to include a ramp into the set of coordinated ramps. In this contribution an approach is put forward to make an adequate decision on which ramps should be coordinated given the situation at hand. To quantify the resulting ramp and bottleneck delays, cumulative inflow and outflow curves are developed as a function of the involved situation-specific variables. This enables us to determine the optimal set of coordinated ramps beforehand and to gain insight into the effects of the system variables that determine the delays. By means of a test case the effects are illustrated and a worked example is given of finding such optimal set of coordinated ramps. Results show that the duration of the peak period and the size of the capacity drop strongly determine the delay at the bottleneck, and hence the coordination benefits of postponing the moment of the capacity drop. These variables also have a large influence on the minimum required share of ramp traffic to the bottleneck (i.e. break even share), that determines whether it is beneficial to include the ramp into the coordination.

Traffic monitoring for coordinated traffic management—Experiences from the field trial integrated traffic management in Amsterdam

In the first phase of the large-scale field trial integrated traffic management in Amsterdam (acronym: PPA), a hierarchical control approach is used to coordinate the algorithms of the ramp metering installations along a densely used freeway corridor with the intersection controllers along one of the connecting urban arterials. This hierarchical control approach requires a similarly organised hierarchical monitoring approach. This approach is based on several freeway and urban state estimation and prediction techniques. In this contribution we describe and discuss two of these in terms of their underlying rationale and we give some some examples of their application. In the final part of this paper we discuss a number of critical issues that came up in the implementation of these methods in the PPA. These relate to the difficulty of communicating the underlying scientific ideas into practice. They also relate to the fact that some of the underlying (scientific) puzzles have not yet been solved.