sentences:  However, some trains (#s 02, 08, 09, 13, 18, 51, and 52) have been fitted with rubber gangways since 2000, and six trains (#s 43, 45, 46, 48, 49, and 50) contain prototype gangways that were later implemented in the MF 01 stock "(from )".In 2012, train #12 was retrofitted with the MF 01 type gangways upon transfer of the train to Line 4, and in March, 2014, train #01 was retrofitted.Because Line 4 is a much curvier line compared to Line 1, there were also concerns that the interconnecting gangways would become damaged from excessive wear and tear caused by the curvature of the tracks and stations.