The Visibility Pre-Warning System For The Freeway Based On CAN Bus

In the past several decades, expressway has made a considerable progress in many countries of the world, and has made enormous contribution to the development of the national economy. In China, especially, the total mileage of the expressway increases at the speed of thousands of kilometers every year, have already topped 30,000 kilometers at present, the second longest of the world. However, along with all the advantages and convenience is the developing rate of traffic accident occurrence. Because of the high speed and big flow of the vehicles, the totally closed, full-overpass structure of the expressway and the rule that forbid decelerating and parking freely, accidents occur frequently on the expressway when the visibility is low, especially when there are agglomerate fog and sandstorm appearing paroxysmally and stochastically. In other words, the most important factor that caused traffic accident on the expressway is the low visibility, which is depressed by local or regional weather status such as agglomerate fog, rain, snow and sandstorm. So design and develop a set of low cost in our country, the high-performance early warning system of visibility It has very good practical value and extensive application prospect that design a visibility pre-warning system, which is low cost and the high-performance, on the expressway in China.Considering the characteristic of the momentary agglomerate fog, sandstorm and the expressway itself, therefore, we suggested a new kind of visibility pre-warning system for the expressway, which is based on CAN bus. The pre-warning system is made up of measuring nodes and communication bus. At the measuring nodes are long-distance photoelectric sensors, which are designed for the long-distance air sampling. A precision phase lock-in detecting circuit is designed to detect the faint optical signal under the controlling of the microcomputer. In virtue of the advantages of the CAN bus, meanwhile, we can form a long distance network, and the measuring signal as well as the controlling signal can be transmitted between sensor nodes and controlling node in real time and at low cost. Then we can monitor the visibility status of whole expressway in time all-day.At first, the thesis introduces the theory and realistic meaning of the visibility pre-warning system of the expressway and then pays more attention to the researching and comparing and analyzing of the present system. According to the result of the comparing and analyzing, the integrated design of the system is presented, and then,...