POLICE INTERVENTION CAN POTENTIALLY MAKE MOTORWAYS SAFER BY CHANGING THE BEHAVIOR OF DRIVERS. HOWEVER, RELIABLE AND UP TO DATE INFORMATION ON VISIBILITY MUST BE AVAILABLE AT POLICE CONTROL ROOMS IF THE BEST USE IS TO BE MADE OF THE LIMITED POLICE RESOURCES. EQUIPMENT TO MONITOR VISIBILITY WAS DEVELOPED UNDER CONTRACT TO THE HOME OFFICE AND CONSISTED OF TWO DEVICES: (1) A POINT VISIBILITY METER (PVM) WHICH MEASURES THE DENSITY OF FOG AT THE CENTER OF THE INSTRUMENT AND (2) A BACKGROUND LIGHT METER (BLM) WHICH IS SIMILAR TO THOSE USED IN PHOTOGRAPHY. THESE TWO INSTRUMENTS ARE USED IN CONJUNCTION SO THAT THE CALCULATED VISIBILITY PROPERLY REFLECT THE PERCEPTION OF OBJECTS IN FOG. TRIALS WERE CONDUCTED TO ASSESS BOTH SCIENTIFIC AND OPERATIONAL ASPECTS OF THE SYSTEM. PRELIMINARY TRIALS LED TO A CLEAR SET OF RECOMMENDATIONS FOR FUTURE FOG WARNING SYSTEMS INCLUDING AN UPDATED SIMPLIFIED DISPLAY, AUTOMATIC RECORDING OF DATA FOR ANALYSIS, RECORDING OF OTHER METEOROLOGICAL DATA SUCH AS WIND SPEED, AND A TRAFFIC MONITORING FACILITY TO STUDY RELATIONS BETWEEN SAFE DRIVING SPEED AND VISUAL RANGE. THE ENHANCED SYSTEM, WHEN OPERATIONAL, WILL OFFER IMPROVED PERFORMANCE AND WILL PROVIDE INFORMATION ON TRAFFIC BEHAVIOR, AND MONITOR THE EFFECTIVENESS OF POLICE TACTICS IN ACHIEVING A SAFE FLOW TO TRAFFIC IN THE FOG. TABULAR DATA AND REFERENCES ARE PROVIDED. (MJW)