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.
- 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.
The benefit-cost ratio reflects the ratio between the socio-economic impacts of the system and total expenses of the system. The remunerative rate of interest indicates how effective the use of invested capital has been. It was estimated that the benefit-cost ratio of the experimental roadway is 1.1 and the remunerative rate of interest is 14 percent. These values indicate that the benefit of the system exceeds the capital costs and that the system has been socio-economically profitable. When optimistic assumptions were used, the benefit-cost ratio was believed to be 1.6. When pessimistic projections were considered, this ratio was 0.6. The remunerative rate of interest ranged from five to 22 percent. Additionally, survey results indicated that the signs were well perceived and remembered, with 90 percent of survey drivers deeming the variable speed limit signs useful.
NotesThe equations used to calculate socio-economic costs are based on the principles determined by the Development Centre of FinnRA. Impacts on average speeds and accident rates were estimated based on information available from other sources, as real effects were not known. The Technical Research Centre of Finland is researching the real impacts in order to conduct a more precise evaluation.
Weather Controlled Road and Investment Calculations
Author: Yrjö, Pilla-Sihvila and Lähesmaa Jukka
Published By: Southeastern Region, Finnish National Road Administration
Source Date: December 1995
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Typical Deployment Locations
VSL, DMS, CMS, VMS, Changeable Message Signs, Variable Message Signs