West Virginia’s Fog Detection and Warning System Was Estimated to Result in a Benefit-Cost Ratio of 1.57, Based on Crash Data.

Efficiency of an Active Fog Detection and Warning System in West Virginia Demonstrated Through Benefit Cost Analysis.

Date Posted

Fog Detection for Interstate and State Highways

Summary Information

Effective fog detection and warning systems could help reduce adverse impacts of fog on safety along roads where fog is a major issue. The goal of this study was to evaluate the feasibility of deploying a new active fog detection and warning system in West Virginia, in addition to the one and only existing active system as of 2012, installed on I-64 Kanawha River Bridge. The system contains Roadway Weather Information System (RWIS), variable message signs (VMS), fiber optic cables, Closed Circuit Television (CCTV), inductive loop surveillance, environmental sensor station, and Highway Advisory Radio (HAR). Through a benefit cost (B/C) analysis justification, efficiency of fog detection and warning system was demonstrated, using data obtained from US DOT, State DOT's, FHWA, National Weather Service and several companies working in the traffic control and warning systems field. Benefits were represented as savings in the number of fog related accidents. Cost estimates were based on a previous report by USDOT RITA published in 2008.


The study assessed the viability of a proposed active fog detection and warning system by determining the B/C ratio. The reduction in accidents was considered as the only benefit derived from the system, due to limited empirical data on other potential benefits. Given that the annual cost of motor vehicle occupant crashes in West Virginia is $88 million, and that fog causes one percent of these crashes, the annual cost attributed to fog-related crashes is $0.88 million. Using a present value factor of 8.11 for a four percent rate over a 10-year service life, the net present value of benefits for a 10-year span is computed by multiplying the annual cost of fog-related crashes ($0.88 million) by the present value factor (8.11) at a four percent rate.


  • Using the estimated cost values in combination with the estimated benefits, B/C ratio of the fog detection and warning system was estimated as 1.57, assuming a ten-year service life. 
  • For a ten-year service life for the fog detection and warning system, the net present value of benefits was estimated as $2.85 million (in 2012 dollars) due to the reduction in number of accidents.
  • This B/C ratio value was estimated to be as high as 2.14, when a service life of 25 years was assumed for the planned fog detection and warning system. 
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