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.
Date Posted

Weather Controlled Road and Investment Calculations

Summary Information

The Finnish E18 Weather Test Area is an experimental road section along the southern coast of Finland between the towns of Kotka and Hamina. The 8.7 mile (14 km) test area is equipped with a road weather information system (RWIS) consisting of 36 variable speed limit signs, five variable message signs (VMS) displaying graphical and textual information, and two environmental sensor stations (ESS). Each ESS measures wind speed and direction, air temperature, pavement and sub-surface temperature, humidity, precipitation rate and accumulation, and pavement condition. The western ESS nearest the sea also measures precipitation type and visibility. Kotka Maintenance Station personnel have primary control responsibility for the system. The Road Monitoring Center at Kouvola monitors the roadway as well. Variable signs are automatically controlled by the RWIS or manually controlled by operations personnel. Manual control is used if the variable signs automatically display information that does not correspond to actual conditions. Variable speed limit signs are divided into 12 separately controlled groups, with signs in a single group displaying the same speed limit. A 15-minute time lag is utilized so that speed limits do not change over short time intervals. The western and eastern parts of the roadway are also controlled separately.
  • The divided roadway section typically has speed limits of 75 mi/h (120 km/h) in the summer. In the winter, recommended speed limits vary between 50 mi/h (80 km/h) and 62 mi/h (100 km/h) based on road and weather condition data collected from the ESS. Recommended speed limits are based on pavement condition, precipitation, visibility and wind. Heavy precipitation and wet pavement conditions reduce the speed limit from 62 mi/h (100 km/h) to 50 mi/h (80 km/h). Visibility below 920 feet (280 meters) reduces the speed limit to 62 mi/h (100 km/h). Visibility below 590 feet (180 meters) further reduces the speed limit to 50 mi/h (80 km/h). When wind velocities exceed 27 mi/h (12 m/s) and 38 mi/h (17 m/s), the speed limit is dropped to 62 mi/h (100 km/h) and 50 mi/h (80 km/h), respectively. When speed limits are reduced, VMS display the reason for the reduced speeds. Three symbols indicating “slippery road surface,” “hazardous conditions ahead,” or “road construction ahead” may also be displayed on VMS. If speed limits are not reduced, VMS display only air and pavement temperatures.
  • The Finnish National Road Administration (FinnRA) evaluated the profitability and effectiveness of the road weather information system based on estimates of socio-economic impacts and 300 driver surveys. The socio-economic factors are costs due to accident, time, vehicle, emissions (i.e., exhaust fumes), noise, and pavement surface. The costs were estimated before and after installation of the RWIS to determine the differences, which represent the socio-economic impacts of the system. Accident rate and average speed were estimated in both summer and winter, and at three speed limits: 75 mi/h (120 km/h), 62 mi/h (100 km/h), and 50 mi/h (80 km/h). The unit value of time was estimated for both light and heavy vehicles. Unit values of fixed and variable vehicle costs were specified for basic conditions. Basic vehicle costs were then estimated based on average speed and comparative fuel consumption. The unit value of emission costs due to nitrogen oxides, hydrocarbons, and particles was calculated. The effect of noise costs was determined based on the change in average speed. Annual asphalt pavement surfacing costs were calculated based on percent change in wearing speed.

Because absolute values could not be used, three assessments (pessimistic, probable and optimistic) of average speeds and accident rates were made. Based upon investment costs of roughly $1.3 million (8.2 million Finnish marks) and annual operation and maintenance costs of approximately $56,000 (360,000 Finnish marks), it was estimated that the average speed decreased 0.4 to 1.4 percent due to the RWIS. The average yearly accident rate was projected to decrease by eight to 25 percent. This impact on safety is due to lower average speeds when accident risk is greatest (i.e., when poor road conditions exist). It is anticipated that annual costs will likely decrease nearly $234,500 (1.5 million Finnish marks).
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