Igicuruzwa cya spiral gikonjesha gifite imiterere yihariye yumubiri, imikorere ya mashini ikora neza ni nziza, imbaraga zo gukanda, umuyoboro ushyinguwe munsi yimiterere, umugozi wimbere wimbere ukikije ubukonje kandi ukarinda neza umutekano wumugozi.