Overview
Changeable message signs (CMSs), sometimes referred to as dynamic message signs or variable message signs, are being used nationwide to provide real-time information to drivers. Among the messages displayed are time-related messages. The following five time-related approaches are available for display on CMSs when a freeway or a tollway is the driver's primary facility: (1,2)
1. Travel Time on the freeway/tollway,
2. Comparative Travel Times on the freeway/tollway and alternate route,
3. Time Saved by taking an alternate route,
4. Delay on the freeway, and
5. Delay Avoided by taking the alternate route.
Travel time and delay messages displayed on a CMS refer to the freeway or tollway only. Conversely, comparative travel times, time saved and delay avoided presume that an alternative route exists and refer to a difference in travel times between the freeway/tollway and the alternative route. The five types of messages are described further in the paragraphs that follow. It should be noted that the issues discussed for each form of time-related information also apply for other travel scenarios such as pre-trip planning. (1,2)