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Speed Feedback Signs Manage to Reduce Mean Speed by up to 2.9 km/h in European Urban Environment.

Study assesses the effectiveness of speed display signs in low-speed urban areas in Finland.

Date Posted

Effects of speed display signs on driving speed at pedestrian crossings on collector streets

Summary Information

Reducing average traffic speed is one of the most effective ways to improve roadway safety. However, simply lowering speed limits is not always effective at reducing speed as drivers may not be aware of their speed or they may choose to ignore posted speed limits. To improve adherence to posted speed limits, public authorities have employed a variety of strategies for reducing speed such as changes to the built environment (e.g. speed bumps) or ITS focused solutions such as speed cameras.

One specific speed reduction ITS solution is speed display signs. Speed display signs utilize radar to detect a driver’s speed. The signs then display the speed to the driver on a roadside sign. Often if the driver is over the speed limit, the sign will flash or display a message such as “Slow Down.”  

For the study, speed display signs were installed along busy and quiet streets in two Finnish cities. Each of these signs displayed the driver’s speed and a graphic symbol that varied depending on the speed of the driver.

  • If the driver was driving at or near the speed limit, the sign displayed a green smiley face.
  • If the driver was driving up to 10 km/h over the speed limit, the sign displayed a red frowning face.
  • If the driver was driving more than 10 km/h over the speed limit, the sign displayed a red exclamation point.

The research team monitored the average speed of traffic on the streets for 1 week prior to installation and for 5 months after installation. Finally, the team removed the signs and monitored average speed for 1 week with the signs un-installed.

The project produced the following findings:

  • The speed display signs resulted in statistically significant drop in speed at three of the four sites. The fourth site that had streets with the lowest traffic volumes saw no significant reduction in speed.
  • The mean speed for all vehicles, across both road types, dropped by 0.5-2.9 km/h (0.3-1.8 mph).
  • Even after the team removed the signs, speed reductions persisted, suggesting that speed display signs are a long-term solution to reduce speed on urban arterials.
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