Characteristics of variable speed limit systems

Abstract

The control algorithm used for deciding on the speed limit in variable speed limit systems is crucial for the performance of the systems. The algorithm is designed to fulfil the purpose of the variable speed limit system, which can be one or several of the following aspects: increasing safety, increasing efficiency and decreasing environmental impacts. Today, many of the control algorithms used in practice are based on fixed thresholds in speed and/or flow. Therefore, they are not necessarily reflecting the current traffic conditions. Control algorithms with a greater level of complexity can be found in the literature. In this paper, four existing control algorithms are investigated to conclude on important characteristics affecting the performance of the variable speed limit system. The purpose of the variable speed limit system and, consequently, the design of the control algorithm differ. Requirements of the investigated control algorithms are that they should be easy to interpret and the execution time should be short. The algorithms are evaluated through microscopic traffic simulation. Performance indicators related to traffic safety, traffic efficiency and environmental impacts are presented. The results show that the characteristics of the variable speed limit system and the design of the control algorithm will have effect on the resulting traffic performance, given that the drivers comply with the variable speed limits. Moreover, the time needed to trigger the system, the duration and the size of speed limit reductions, and the location of the congestion are factors of importance for the performance of variable speed limit systems.

An Exploratory Qualitative Study of the Prevention of Road Traffic Collisions and Neurotrauma in India: Perspectives From Key Informants in an Indian Industrial City (Visakhapatnam)

“…As one of the countries with the highest populations globally, it was no surprise that overpopulation was raised as another challenge to RTCs and neurotrauma prevention [70]. An overpopulated area tends to have high vehicular tra c on roads which if uncontrolled by law enforcement has shown to promote unsafe behaviour, thus leading to RTCs [71][72][73] Although controlling population growth is another ongoing government agenda, immediate measures to overcome this issue were as suggested by participants, namely through variable speed limits, providing separate lanes for slow and fast-moving vehicles and optimising tra c-light management, in addition to changing driver behaviour through education and awareness efforts and enforcing laws to ensure safe road use [73,74].…”

Evaluation of a Mobile Highway Management System at Roadwork Zones

“…However, the impact is demonstrated on a microscopic traffic simulation model in PTV Vissim. While authors explain the calibration procedure, their own experience in demonstrating the effects of speed harmonization is strongly dependent on drivers' compliance [16] and the results cannot be compared to real-world studies (as presented in this paper). Similar results were also discussed in literature [17][18][19].…”

Influence of Spatial Placement of Variable Speed Limit Zones on Urban Motorway Traffic Control

“…Two main strategies used in VSL systems are speed harmonisation and traffic breakdown prevention [2]. The contribution of speed harmonisation lies in reducing the speed variance between vehicles within the lane and between the lanes.…”

“…Such speed deviations often form shockwaves that propagate upstream regarding the mainstream traffic flow [1]. Thus, mainstream flow becomes unstable and less safe [2]. The Level of Service (LoS) of the urban motorway is then reduced which in term decreases the effective motorway capacity and average speed, increases traffic density and Travel Time (TT).…”