3 Speed Management
3.2.7 F-6 Driver Aid System – New South Wales, Australia
Impetus for the Activity
A 12-km section of F6, the main freeway between Sydney and Wollongong, frequently experiences highly variable fogs where visibility can vary from clear to below 100 m and back again within 1 min of driving.
Criteria for System Selection (Hardware and Software)
The selected system was based on a previous trial of a Vaisala fog detection unit connected to a fiber optic VMS, which had shown a substantial reduction in speeds during daytime fogs.
Description of the System
The system was installed in 1993 to avoid rear-end collisions in fog and is currently active. The system has 24 VMSs, 12 for each direction, including 1 for advance warning. The signs are erected on gantries and have flashing lights attached to them. Each sign is connected to road loops and a visibility detector.
Vehicle speeds are monitored to assess if the speed differential between successive vehicles is in excess of the available sight distance. When it is in excess, vehicles are advised of a safer traveling speed for the conditions. These posted speeds are advisory.
Each site has independent computer control, but the sites are linked to a central computer through a radio network. Status reports at each location are obtained every 5 min. When fog occurs, the central computer can place messages on signs outside of the actual fog zone, thereby providing advanced warning of the approaching hazard.
In clear weather conditions, the signs can be used to provide drivers with safety messages or advise them of the speed limit when they are speeding.
System Effectiveness Evaluation
Data is being collected to perform a safety evaluation of the system.