The green buses are the Guaguas Urbanas that run the interior lines in Arrecife. Anyone can jump on them and pay a fare. There are four lines: http://www.arrecife.es/portal/p_contenedor_index_1v_13_3_3.jsp?seccion=s_fdes_d4_v2.jsp&codbusqueda=48&language=es&layout=p_20_contenedor1.jsp&codAdirecto=24&codResi=2