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Road Weather Management > Traffic Control > Variable Speed Limits


Variable speed limit systems use sensors to monitor prevailing traffic and/or weather conditions, posting appropriate enforceable speed limits on dynamic message signs.


Icy Curve Warning Systems in California reduced the number of annual crashes by 18 percent, and the system was estimated to provide safety benefits of $1.7 million dollars per winter season.(June 2012)

Using a Speed Management System for winter maintenance resulted in zero (100 percent reduction) winter weather related accidents in one section of highway in Snowmass Canyon.(June 2012)

Variable Speed Limit System shows promise; crashes reduced to lowest level in a decade.(October 2010)

In Finland, a benefit-cost analysis supported the deployment of weather information controlled variable speed limits on highly trafficked road segments.(25 March 2006)

In Salt Lake City, Utah the ADVISE fog warning system tested on a two-mile section of I-215 promoted more uniform traffic flow, reducing vehicle speed variability by 22 percent while speeds increased 11 percent.(June 2003)

A study of travelers on Snoqualmie Pass, WA found that DMS can decrease mean driving speeds and reduce accident severity.(December 2001)

In Tennessee, a fog detection and warning system implemented in 1994 significantly improved safety as no fog-related accidents have occurred since implementation.(October 2000)

In Finland, road weather information posted on dynamic message signs was well perceived and remembered by surveyed drivers; 90 percent deemed variable speed limit signs useful.(December 1995)

In Finland, a road weather information system with variable speed limit signs was projected to decrease the average vehicle speed by 0.4 to 1.4 percent and reduce the annual crash rate by 8 to 25 percent.(December 1995)

In Finland, a road weather information system with variable speed limit signs was projected to yield a benefit-to-cost ratio ranging from 0.6:1 to 1.6:1 depending on the influence of the system on vehicle speeds and crash rate.(December 1995)

On the A16 Motorway in the Netherlands, an automatic fog warning system prompted drivers to slow down by 8 to 10 km/hr and drive at more uniform speeds; however, during extremely foggy conditions the system increased the average vehicle speed by 31 km/hr matching the recommended speed.(1995)

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