Low visibility is one of the most serious meteorological factors affecting road traffic. Along with the technology development of digital camera and image recognition and the information shared among the meteorological and traffic departments, using camera video data along the expressway to rapid recognize the visibility becomes an important method to improve the precision of visibility temporal and spatial monitoring. In this paper, we propose a daytime road image visibility detection method based on the brightness contrast and dark channel prior principle: (1) to extract the interested road domain according to the Hough transform detection method, (2) by using the brightness contrast method, the farthest pixel point that the human eye can distinguish is used as the target point, (3) to evaluate the transmittance of the target point based on the dark channel prior principle, (4) to figure out the image visibility value by the relationship between visibility and extinction coefficient. The test indicators of this paper are visibility absolute error and visibility level error. The test data is derived from the video image data of the Wuyu section of Jingtai Expressway in Anhui Province and the NingguoHutong section of Ningji Expressway in Anhui province, and the visibility data set of the traffic weather stations near the expressway in Anhui Province. The results indicate that the method can accurately reflect the trend of visibility change, and the detection accuracy can be as high as 95%, which can be a good reference for the image visibility recognition.