The Low Visibility Detection And Pre-Warning System For The Freeway

Because of the high speed and great flow of the vehicles on freeway, accidents occur frequently when the visibility is low, especially when there are agglomerate fog and sandstorm which appears paroxysmally and stochastically. Low visibility, which is caused bad weather such as agglomerate fog, rain, snow and sandstorm, has become the main cause of traffic accident on the freeway. It has become an urgent task to develop a visibility pre-warning system to improve the road security.This thesis developed a visibility sensor measure and pre-warning system, which contains a visibility sensor, a data processor and signposts. The visibility sensor measures the visibility of the freeway in real time and sends the visibility data to the data processor, which make the signposts flash to warn the drivers when the visibility is lower than a threshold.This thesis first introduces the theories of visibility measure and studies made in the field. Then the VJC-2 type forward-scattering visibility sensor, which consists of transmitter, receiver and signal processor. The transmitter transmits a low frequency light pulse, which is received by the receiver setting at 33 scatter degree after scattered through atmosphere. The pulse signal is then amplified by AGC and converted to digital signal by A/D IC. Then the signal processor detects the scattered signal from the digital signal by correlated detection. Finally, the visibility is computed based on expressions of visibility detection. Experiments on freeway have demonstrated that the visibility sensor is of high preciseness and stability.A pre-warning system based on solar energy is also proposed in the thesis. The pre-warning system sends pre-warning orders to the wireless signposts, which flash in different models to inform the drivers the visibility of the road ahead. Application of the system can effectively improve the road security.