Dense fog has often been a cause of tragic road accidents. The development of a cost-effective highway visibility sensor which communicates road visibility data to a host ITS (Intelligent Transportation System) is proposed for DOT 94-FH7. The ITS then provides warnings to motorists through roadside displays or radio communication directly to the vehicle. Technical feasibility of the proposed optical sensor, which measures scattered light from fog and dust particles, was confirmed in Phase I. A test program is proposed for Phase II to build a number of engineering prototype sensors and install them in several selected field locations for extended testing. A detailed outline of the proposed field sensor design is presented. Provisions for self-test, self-calibration, and contamination compensation are outlined. Communication with the host ITS system will be implemented using both fiber optic and cellular phone hardware. The novel, compact sensor is expected to have dramatically lower life-cycle costs than existing sensors, including acquisition, installation, and maintenance costs.Anticipated Results/Potential Commercial Applications of Results:The proposed project will result in establishing an inexpensive, low maintenance visibility sensor. The sensor would be applicable to many Federal Government and industry applications in addition to its primary use as a fog detection system. These include air pollution monitoring of industrial plants, smoke stacks, and large cities.