The measurements of per minute from 26 automatic transport meteorological stations along the Shanghai〖KG-*8〗〖CD*2〗〖KG-*8〗Nanjing expressway, indicate that both haze and heavy fog weather can affect visibility, but there are some differences in many aspects. Under suitable conditions, they can transform mutually, and there is a coexistent phase between them. It is helpful to recognize these differences and changing conditions for improving low visibility forecasts and traffic services to traffic departments. The causes of uplifting hazes and frequent fogs, as well as the earlier appearing time and longer duration, in hilly and valley areas are analyzed, which will conduce to know the characteristics of local heavy fogs and visibility differences along the expressway. The largescale and continuous heavy fogs are often related with a wide range of hazes. In favorable weather conditions, in night time fogs get denser and visibility becomes lower while there is radiation cooling, and in daytime visibility may improve slightly. These phenomena usually continue for several days before the southward movement of strong cold air.