Field tests are being carried out in cooperation with Maryland and Michigan to implement and analyze the effectiveness of variable speed limits (VSL) in work zones. These projects are a joint effort between Safety and ITS Joint Project Office. The VSL are displayed on portable trailers and rely on input of vehicle speeds, presence of road work activity, and other information to post an appropriate speed limit, allowing motorists to maintain the most efficient and safe speeds, without endangering themselves, other drivers, or workers