In Finland, a benefit-cost analysis supported the deployment of weather information controlled variable speed limits on highly trafficked road segments.
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Country-Wide Variable Speed Limits?

Summary Information

In Finland, approximately 350 km of roadway have been equipped with variable speed limits and most of them are weather-controlled. This study estimated the benefits and costs of expanding the system. Three different size networks were modeled to establish parameters for the cost-effective expansion of the system. Evaluation data collected from previous studies were projected onto the models which ranged in size from 2100 to 4300 km. Each model represented a contiguous network of variable speed limit signs (LED signs) that were controlled automatically by information produced by road-weather sensing stations. The road sections belonging to each network were selected based on set traffic safety and traffic volume criteria. The speed limits displayed were determined according to a control policy formulated by the Finnish Road Administration.

The benefit-cost analysis covered a period of 20 years and assumed an annual two percent increase in traffic and an annual five percent decrease in personal injury accidents. The safety data were derived from previous research. Ancillary impacts on pollution and noise costs were assumed marginal and were not included in the analysis. The system costs input into the analysis included construction and maintenance costs derived from recently built systems and evaluated at the 2004 level.

The implementation plan was designed to accommodate two types of facilities: motorways and dual carriageways (divided highways), and single carriageways (roadways with no physical separation). The following data excerpted from table 2 of the report show the combinations of technologies deployed.


Road type
Speed limit signs
Combined information and warning signs
Traffic monitoring stations
Road weather stations
Traffic monitoring cameras
Motorways and dual carriageways 6 units /graded intersection. If the spacing between intersections is longer than 5km, speed limit repeater signs are required (4 units). One for each carriageway for each intersection spacing Every graded intersection spacing has one traffic monitoring station One for every 15km One for each graded intersection
Single carriageways 4 units /intersection. If the spacing between intersections is longer than 5km, speed limit repeater signs are required (2 units). One for every other intersection spacing One for each 20km One for each 15km One for each 20km

Overall, the results of the benefit-cost analysis were favorable for deployments along highly trafficked road segments. Starting (low-end) benefit-to-cost ratios ranged from 1.1:1 to 1.9:1. Ratios increased for scenarios where higher safety benefits were assumed and control policies allowed for higher speed limits.