In the interstate system, the three digit numbered highways are EXTENSIONS of the main one or two digit highways. These generally re bypasses and connectors. For example, I-695 is the bypass around Washington, DC when you are driving on I-95; I-495 is the Baltimore bypass. Other cities use a spur as an "extension." I-278, including the BQE and the SI express-way, is considered an extension of the east-west I-78, crossing through PA & NJ.
Staten Island WebŪ Forums Index.