Potential Effects of Composition and Structure of Dynamic Message Sign Messages on Driver Behavior and Their Decision to Use Freeway Incident Traffic Management (FITM) Routes
A research team from Morgan State University studied the potential effects of various dynamic message sign (DMS) designs on route choice and driver compliance by reviewing literature and best practices from six states (Virginia, California, Connecticut, New Jersey, Texas, Florida and Oregon) in addition to performing testing of a driver simulator. DMS designs studied varied in content, type, and message length. For the testing, a 155 square-mile road network southwest of the Baltimore metropolitan area was simulated in a driving simulator. Six scenarios (390 simulations total) were conducted with 65 participants; participants were asked to drive from a given origin to a fixed destination. Researchers used simulations to track route choice and assess the impact of environmental factors on travel decisions. A total of eight survey questionnaires (two pre-simulation and six post) were used to gather demographic information and route preference, and to assess driver compliance.
The following lessons learned were summarized based on the driver simulator study and DMS best practices from the literature review.
- Design DMSs to be color-coded (especially color-blind people-friendly) and to provide route avoidance advice to encourage compliance and increase effectiveness in determining route choice.
- Minimize the number of units of displayed information. Display two to three units of information per DMS to increase overall travel speeds and ensure driver comprehension - where one unit of information can be described as an answer to a single question (e.g. What happened?, Where?, What effect on traffic?, Who is the advisory for?, What is Advised?). If more information needs to be displayed, then split it into two phases or DMSs.
- Display single-phase messages and traffic congestion levels in the shape of horizontal bars to help quicker driver or motorist DMS comprehension. The length of the bars show traffic congestion levels, making them friendly to color-blind drivers.
- Design DMSs to provide crash-related information and advice to further encourage driver compliance and adjust driver route choice. In particular, advice that mentions "avoid" tends to have a high compliance rate.
- Travel time messages should only be used in regions or corridors that experience recurring congestion, where traffic conditions are dynamic enough that they are not viewed as static messages. Drivers were found to pay less attention to travel time-related DMS messages when using GPS/smartphone for navigation.
- Provide drivers with specific instructions or advice instead of vague travel messages (e.g. suggest an alternative route instead of just indicating “Expect Delays”).
- Use graphics-aided DMS to help elderly drivers better understand messages. Drivers responded faster to messages displayed with graphical symbols, although with slightly less accuracy than text-only messages for younger drivers.
- Place a DMS in advance of major decision points, such as interchanges or intersections, where motorists can respond to specific information displayed on the DMS. A DMS should be located as close to the edge of the traveled way (ETW) as possible to maximize visibility.