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.
The system has a positive effect on speed choice in fog: it was found to result in an additional decrease of speed of about 8 to 10 kph and a slight reduction in standard deviation of the speed. In extremely low visibility (< 35 m), the system had an adverse effect. The average speed with the system in this situation was 60 kph, versus 29 kph without. Using the relation between mean speed and number of accidents, a reduction of 5 kph would result in a similar reduction in the number of accidents by approximately 15 percent. The system showed small or no effects in other measures of driving behavior such as following distance, time headway, and time to collision.
Evaluation of A16 Motorway Fog-Signaling System with Respect to Driving Behavior
Author: Hogema, Jeroen and Richard van der Horst
Published By: Transportation Research Board
Source Date: 1995
Other Reference Number: TRR 1573
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RWIS, ESS, Environmental Sensor Station, RWIS Station, road monitoring, weather station, environmental sensing station, VSL