참고문헌
- Vance, L., Mattson, P., (1994), Tube Transportation, US Dept of Transportation, Volpe National Transportation Systems Center, Feb.)
- http://www.tubexpress.com/index.htm
- http://www.cargocap.de/html_en/strasse_01.html
- http://et3.com/index.html
- http://faculty.washington.edu/~jbs/itrans/flextaxi.htm
- http://www.tubeway.de