Image of car driving past traffic signs

The idea of fewer—or no—roadside signs holds appeal for highway departments (less maintenance) and drivers (less visual clutter). But if the information typically conveyed on signs—such as the speed limit—is given to drivers in another way, would it be safer? And how would drivers respond?

Researchers at the University of Minnesota’s HumanFIRST Laboratory recently tested how in-vehicle signing could warn drivers of changes in the environment and influence their behavior. Led by RSI researcher Nichole Morris, the project examined how drivers react to in-vehicle sign (IVS) systems designed to prepare them for transitions in driving conditions such as speed zone changes, school zones, construction zones, and curves.

The project, sponsored by the Minnesota Local Road Research Board, arose from a previous Minnesota Department of Transportation study that looked at the feasibility of using smartphones for implementing connected vehicle programs. One of the questions that came out of that study was whether road signage could be eliminated from the roadside and displayed in the vehicle instead. Doing so could save tax dollars related to sign installation and maintenance, improve landscapes, and make it easier to keep signage up-to-date.

Researchers began by developing a simulated route for the HumanFIRST Lab’s driving simulator using a real roadway network from southern Minnesota. Forty participants were asked to drive the 24-mile simulated route (which included freeways, two-lane rural roads, and towns) with and without the IVS system activated. As they drove, performance measures were collected.

The researchers found that an IVS system would affect driving in several ways. When only in-vehicle signs were used, speeding and speed variability increased. “Safety across all crash types was significantly reduced when in-vehicle warnings were used without external signs,” Morris says. 

However, speeds did not increase when both IVS systems and external signs were used, and speed variability declined slightly. “This suggests that as a supplement to external signs, the IVS system might reduce traffic speed variability and improve safety,” she says.

Victor Lund, a traffic engineer with St. Louis County, MN, and the technical liaison for the study, says traffic engineers are concerned about the negative impact on safety of people driving at different speeds. “An IVS system might help reduce speed differentials, and we get really excited when we see something constructive toward that end.”

Another key finding from the study: IVS systems did not appear to distract drivers. ”Sometimes smartphones are the cause of driver distraction,” Morris says. “An IVS system might be a tool to break that distraction by showing the driver there’s something important ahead and to change speed.”

The researchers also evaluated the usability of the technology. Test participants reported that the mental workload required to drive when an IVS was used instead of external signs was greater than under baseline conditions. Driver satisfaction with the IVS was also lower when it was used alone.

Based on the results, the researchers offer several recommendations. “Although using IVS systems instead of external signs would presumably save money on infrastructure costs, we do not recommend this,” Morris says. “However, we do believe that using these systems in conjunction with external signs has the potential to reduce speeding and crashes and needs to be explored further.”

Researchers hope to see this work expanded to examine the role of emerging IVS systems that could deliver important safety information between connected vehicles, such as speeds at intersections and work zones. In addition, understanding how drivers respond to IVS systems could help emergency vehicles create a cleared path and encourage drivers to comply with “move over” laws, Morris says.

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