 State highway officials reached a compromise by opting for an alternative depressed design with an overhead concrete deck connecting Center City to a planned redeveloped waterfront today known as Penn's Landing.By 1979, the entire length of the expressway was open to traffic with the exception of a segment near Philadelphia International Airport.Completion of the final section of the highway faced considerable difficulty, as the road was to be built on a layer of clay separating the city's water supply from the output of its sewage treatment plant.