A Flash Crowd Effect (FCE) occurs when in the case of non-recurring congestion a large portion of drivers follows similar re-routing advice. Consequently, congestion is transferred from one road to another. Coping with the FCE is challenging, especially if the congestion results from a temporary loss of capacity (e.g. due to a traffic incident). The existing route guidance systems do not address FCE, as they either do not consider the effects of guidance on the rest of the road network, or predict link travel times based on the number of vehicles traveling on the link, which in the case of the loss of capacity is unreliable. We demonstrate that the FCE can be addressed in a distributed way route guidance, connected vehicle technology, flash crowd effect.

Realistic simulations of Vehicular Ad hoc Networks (VANETs) are necessary to evaluate novel technologies based on such networks and to prove benefits obtained from their implementation. This survey gathers from several research domains aspects that increase the quality of VANET simulations. It explains a multi-fold nature of VANETs and presents main building blocks of their simulation-traffic and network simulators. The paper proposes a comprehensive architecture for VANET simulation platform that focuses on producing reliable results. The architecture contains traffic and network simulators that communicate with each other in a dynamic and bi-directional way. The concept of a realistic traffic generator is introduced. It uses real-world data (e.g. maps, traffic volume counts) to model an activity-based traffic varying in time. The traffic generator aims at reproducing accurate vehicular traces for urban scenario. A higher level of realism can be obtained by modelling of human behaviour with intelligent agents and by the implementation of related subsystems, like traffic management and control or weather factors.

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Realistic vehicular traces are necessary in reliable VANETs simulations in order to evaluate protocols and applications designed for new technology. Because of the complexity of traffic behaviours, the generation of vehicular traces is one of the biggest challenges in VANETs research. This paper consolidates the current state-of-the art on vehicular mobility generators into three aspects: mobility models, traffic demand model and route assignment method as well as provide and overview of existing generators. The main part of the paper focuses on the improvement of traces generated by the VehiLux model over the city of Luxembourg. The quality of a large set of traces is assessed by the means of realistic traffic simulation and a proposed fitness metric. The influence of the implementation of the Gawron's algorithmroute assignment method on the quality of generated traces is evaluated.

A vehicular Ad Hoc Network (VANET) is a type of wireless network where nodes represent moving vehicles. Some VANET-based applications might require organising vehicles into groups (communities). However, the high mobility of the vehicles and their tendency to travel in clustered flows makes them a challenging subject for community detection. Communities should be formed on the fly, using only local knowledge about their neighbourhood, and evolve as vehicles move over time. The main goal of this paper is to evaluate if stable community detection is possible in highly dynamic VANETs. To do so, the SandSHARC algorithm is extended with two different stability metrics: link duration and mobility similarity. In order to evaluate the stability of the evolving mobile communities, new quantitative and qualitative metrics are proposed, and run simulations on two different VANET scenarios: highway and urban. We analyse how the two stability metrics improve the stability of the detected communities. The results demonstrate that stability depends on the mobility patterns of the underlying traffic network. The proposed method can be applied in a distributed manner and produces communities with robust communication links between members what makes it viable for VANET applications.