Variable Speed Limit Systems (VSLS) where variable message signs show speed limits based on, for example,traffic volume or road conditions exists on motorwaysin many countries. The purpose of the VSLS is to decrease the number of accidents and to increase traffic efficiency. Cooperative systems are a type of intelligent transport system that has received increasing interest lately. The central part of a cooperative system is communication between vehicles and/or vehicles and the infrastructure. In this paper, a cooperative systems extension of a VSLS is proposed and evaluated by means of traffic simulation. By adding cooperative systems functionality to an existing VSLS there is a potential for further increase in traffic efficiency and also to reduce the environmental impacts of the traffic on the road. In the proposed cooperative VSLS, communication between the vehicles and the infrastructure is made available via a roadside unit communicating the speed limits to vehicles upstream on the road. The results of the study show that the cooperative VSLS has a potential to contribute to flow harmonization and to reduce environmental impacts.