News

Traffic Sign Life Expectancy Research Project

While local organizations have always been encouraged to maintain their traffic signs, a June 2014 ruling now requires public agencies (cities, counties, and the Minnesota Department of Transportation) to develop and implement a comprehensive sign maintenance program. But how long do traffic signs really last? Existing data suggests sign life actually exceeds the manufacturer’s warranty. While several sign life analyses have been started, none of the studies has produced conclusive results. To answer this question, the Minnesota Local Road Research Board (LRRB) has funded a new research project to develop expected sign life values, enabling local agencies to better manage their traffic sign assets and implement cost-efficient sign replacement strategies.

As part of the research project, MnDOT researchers have installed a test deck (sample signs with known information including age and previous location) at the MnROAD Research Center. A research team will use this test deck to study retroreflectivity (visibility) and color readings over time to eventually determine the life of sign sheeting material. Initial data collected so far suggests a reasonable sign life expectancy of 12 to 20 years for beaded sheeting and 15 to 30 years for prismatic sheetings. Researchers will continue to update these values and determine a definitive expected sign life as more information becomes available from the test deck. In the meantime, agencies are encouraged to at least adopt a sign maintenance method.

For more information regarding traffic sign life expectancy (including recommendations and best policy practices), please visit the following resources:
•  MnDOT project site
•  LRRB full report 
•  YouTube video:

August 19, 2014

New LRRB YouTube Videos Available Online

The Minnesota Local Road Research Board (LRRB) has recently produced several new YouTube videos, which are available on the MnDOT Research Services YouTube channel. Video descriptions and links are also included below.

What is the LRRB?
Learn how the LRRB supports and shares the latest transportation research applications with the state’s city and county engineers.

Answers to Common Questions about Gravel Roads
More than half of U.S. roadways are gravel roads, making them an important part of our transportation system. Learn about gravel road construction, common problems with gravel roads, and how to keep a gravel road in the best condition.

Construction Zone Safety: Our Responsibility
Scott Gabrio, a MnDOT maintenance worker who was seriously injured by a distracted driver in a construction zone, shares his story and discusses how we can prevent similar accidents from happening in the future.

De-Icing Study: Putting the Products to the Test
Watch as MnDOT-funded researchers transform the parking lots of Valleyfair and Canterbury Park in Shakopee, Minn., into driving tracks to study the effects of weather and vehicle traffic on different deicing treatments.

Frost Damage in Pavement
Frost-damaged roads can be a major pain (and expense) for public works agencies and road users. Learn the major causes and cures of frost damage.

Minnesota Bike Lanes: Learning to Share
Join the discussion as we talk with pedestrians, cyclists, and motorists in Minnesota to identify some common misconceptions about bike lanes.

Navigating a Multi-Lane Roundabout
This video shows drivers how to navigate a multi-lane roundabout and what to do when large vehicles and emergency vehicles are traveling through the roundabout.

Road Closed Signs: Beware and be Aware
Learn the dangers of entering a construction area and the importance of obeying Road Closed signs.

Sign Life Expectancy Research Project
Researcher Howard Preston explains what MnDOT is doing to learn the life expectancy of traffic signs.

Why Aren’t They Working on My Road?
Ever wonder why your road isn’t being repaired? This video explains why roads go bad and why the worst roads are sometimes the last to be fixed.

June 12, 2014

Impact of Flashing LED Stop Signs on Crash Reduction

In an effort to improve safety at stop sign-controlled intersections, several communities have installed flashing LED stop signs at select intersections throughout the state. Researchers are optimistic that because stop signs enhanced with flashing light-emitting diodes (LED) are more visible to drivers, they will hopefully reduce the number of right-angle crashes. Given the statewide interest in this strategy, the Local Road Research Board conducted a study to evaluate the impact of flashing stop signs on safety and driver behavior.

Initial research confirms at least some safety benefit to the signs. For example, the statistical analysis of 15 intersections predicts that installing flashing LED stop signs can reduce the frequency of right-angle crashes by nearly 42 percent. (It is important to note that with a 95 percent confidence interval, it is impossible to state the magnitude of crash reduction with statistical certainty; this reduction could actually be anywhere between zero and 71.8 percent.)

Field studies using portable video equipment also indicate that at intersections with LED signs, drivers were much more likely to stop when opposing traffic was present (10.6 clear stops for every clear nonstop after installation compared with 4.2 stops for every nonstop before installation). When no opposing traffic was present, however, there was no change in behavior after installing the flashing LED sign; approximately four drivers did not clearly stop for every driver who did stop.

While no further research is planned, MnDOT will continue to monitor the intersections with flashing LED stop signs to collect more data about their impact on safety. To learn more, click here and view the full report. 

May 23, 2014