University of Minnesota identifies design alternatives for rural warning signs


Researchers at the University of Minnesota (UMN) have helped the Minnesota Department of Transportation (MnDOT) improve the Rural Intersection Collision Warning System (RICWS) that has been deployed across the state to aid motorists safely cross Stop junctions.

In an effort to reduce dangerous right-angle crashes at rural intersections, MnDOT has deployed dynamic warning signs at approximately 52 sites throughout the state. Using sensor technologies, the signs provide real-time traffic information to motorists at non-signalized intersections where cross traffic does not stop, warning drivers on the minor road when it is unsafe to enter the intersection.

However, a number of sign-related complaints have been received from local road users. To address this issue, UMN human factors researchers studied the current sign to identify what features or layouts may be problematic, and propose safe and efficient alternatives.

The research team first surveyed Minnesota county engineers regarding their experiences and perceptions, as well as complaints or comments from local road users. Through iterative usability studies, the team then examined alternative designs to produce three sets of sign options for a driving simulation study. A total of 120 participants evaluated the safety effectiveness and efficiency of the sign options among teen drivers, middle-aged drivers and older drivers.

Compared with the original sign (left column of illustration above), the proposed alternative (right column) might offer comparable safety benefits, but fewer potential risks. The sign consists of three different sign states: ‘Don’t cross/turn’ (top); ‘Sign is on/operating and no traffic is detected’ (middle); and ‘Sign is off/inoperable’ (bottom).

The warning system’s benefits varied among the three age groups: middle-aged drivers demonstrated the most potential for safer gap acceptance; teenage drivers did not appear to be significantly assisted by the warning system, despite their self-reporting that the sign assisted them; and older drivers tended to have a significantly reduced risk of accepting an unsafe gap, but were also less efficient in using the system, as they waited longer and rejected safe gaps more frequently.

After reviewing the study results, researchers identified an alternative sign design for future field tests that may demonstrate comparable safety benefits to the original sign with fewer potential risks. Specifically, certain design elements, an action word or icon, were recommended for consideration in follow-up field evaluations and future implementations. The findings may also have a broader implication for the design, development and implementation of effective intersection countermeasures on rural, urban and suburban roadways.

“We directed special emphasis to the most vulnerable driver populations, such as older drivers and novice teenage drivers,” said Nichole Morris, director of UMN’s HumanFIRST Laboratory and the study’s principal investigator.

The results indicated an overall safety benefit of sign deployment said Morris said: “All the sign options except for one, enhanced drivers’ gap-acceptance performance. At intersections with inadequate sight distance, gap acceptance tended to be significantly better.”

Ray Starr, acting state traffic engineer at MnDOT’s Office of Traffic Engineering, commented, “Intersection warning systems are an important tool for us as we push toward having zero deaths due to traffic crashes. This study provides valuable information that is helping us consider any design changes for future versions of the warning system.”

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Adam joined the company in 1994, and has been News Editor of TTT since 2009. In his other role as Circulation Manager, he helped create the original Traffic Technology International distribution list 23 years ago, and has been working on it ever since. Outside of work, he is a keen fisherman, runs a drumming band, and plays an ancient version of cricket.