The Staten Island Ferry is the world's busiest ferry route, carrying approximately 20 million passengers on the 5.2-mile (8.4 km) route between Staten Island and Lower Manhattan and running 24 hours a day. Other ferry systems shuttle commuters between Manhattan and other locales within the city and the metropolitan area.

Answer this question, if possible (if impossible, reply "unanswerable"): In kilometers, how long is the Staten Island Ferry route?
8.4