1. 1) Traffic Bureau in the National Police Agency, "Installation status of roundabouts (As of March 31, 2022)," <https://www.npa.go.jp/bureau/traffic/seibi2/kisei/roundabout/0403kanjoukousaten.pdf> (accessed 24 March 2023) (in Japanese).
2. 2) "Special supplement/Practical application of safe and ecological roundabouts in Japan," Int. Assoc. Traff. Safe. Sci., 39, pp. 4–74 (2014) (in Japanese).
3. 3) Japan Automobile Manufacturers Association, "Special feature: Roundabouts that is non signal-regulated intersection," JAMAGAZINE 2014, 48, pp. 2–14 (2014) (in Japanese).
4. 4) Japan Society of Traffic Engineers, Roundabout Manual (Maruzen Publishing, Tokyo, 2016) (in Japanese).
5. 5) Ministry of Land, Infrastructure, Transport and Tourism, Roundabout Study Committee, <https://www.mlit.go.jp/road/ir/ir-council/roundabout/index.html> (accessed 24 March 2023) (in Japanese).