End Of Congestion Research Articles

Deflagration to detonation transition in a vapour cloud explosion in open but congested space: Large scale test

The paper reviews large scale experiments with various fuels in air where successful deflagration to detonation transition (DDT) took place. This includes a recent experiment disclosed in the Buncefield R&D program, where DDT developed in the propane/air mixture. The DDT occurred in branches of deciduous trees in a premixed stagnant mixture. An internal R&D investigation programme was initiated to better understand the phenomena. A large scale experiment in an open space with ethane air mixture is presented in the paper. The premixed mixture was ignited at the edge of the congested three-dimensional rigs which consisted of vertical and horizontal pipes. After ignition, the flame accelerated in the congestion and transitioned to detonation at the end of congestion. Stable detonation propagated through the remaining open and uncongested space.The flame acceleration process leading to DDT is scale dependent. It also depends on many parameters leading to a large investigation array and, significant cost. However, such R&D efforts aimed toward a safer plant design, i.e. the prevention of occurrence of a major accident, are a small fraction of a real accident cost.

Improving Traffic Flow Efficiency by In-Car Advice on Lane, Speed, and Headway

This paper presents a new in-car advisory system that gives advices on lane, speed, and headway. The advices are determined at a traffic management center based on a new lane level traffic state prediction model, in order to prevent or solve suboptimal traffic flow conditions. The system aims for an optimal lane distribution in high flow conditions, decreasing the chance of spillback by advising drivers away from the right lane, and a reduction in the capacity drop by advising drivers to maintain a short (but safe) headway at the end of congestion. The system is implemented in microscopic simulation to evaluate the potential benefits for different penetration and compliance rates. Benefits at both low and high rates are found as only a small redistribution of traffic over the lanes may be required to stabilize flow. The capacity drop is mainly reduced at high rates as it is required that many vehicles accelerate more. The maximum benefit found is a reduction of 49% in travel time delay. Effects are smaller at lower rates. Negative side effects are also found, including oversaturation of lanes partially by advised lane changes and increased probability of spillback taking effect.

Real-Time Queue-End Detection on Freeways with Floating Car Data

This paper is a contribution toward an operational use of large floating car data in traffic management. The work focused on a practice-ready approach on highways. The goal was to detect in real time the end of a perturbation. As an entire highway network is not fully equipped with cameras or loop detectors, floating car data have the potential to help detect the end of a moving bottleneck better. This specific zone represents a significant road safety risk. Better real-time detection of the end of congestion is needed. To address this issue, real-world data were analyzed from a French freeway with recurrent congestion patterns. After the quality and the precision of floating car data were discussed, a dynamic spatial segmentation of the network highlighted the relevance of this data source from an operational standpoint. In addition to the empirical network characterization, a systematic detection algorithm able to detect the queue end in real time with a 500-m precision was introduced. Assuming a growing penetration rate of floating car data, the algorithm used only floating car data with simple detection rules and few parameters. The method was validated on real congestion cases. Results proved the accuracy of the detection. The paper discusses the precision of floating car data, and recommendations for road operators are introduced.

The Existence of a Time-Dependent Equilibrium Distribution of Arrivals at a Single Bottleneck

The paper gives conditions which guarantee the existence of an equilibrium arrival pattern at a single bottleneck. In the model, the times at which a driver wishes to leave the bottleneck depend on the driver. The equilibrium queue length in this model always has a continuous time derivative everywhere. However, the slope of the equilibrium cumulative arrival distribution is discontinuous at the beginning and end of congestion.