Mk I Stock trains that were used on the line, the first trains arriving in 1998. These trains are similar, composed of long cars with externally hung doors, but with differing traction equipment. OPO operation was introduced on the Northern line with the new trains. The last service with a guard operated on the London Underground in January 2000. On the Jubilee line a seventh car was added to trains in 2006. A new signalling system allowing automatic operation was commissioned in 2011. On the Victoria line, new trains were introduced between July 2009 and June 2011. A new signalling system has allowed 33 trains per hour from January 2013. Isle of Wight Although the Isle of Wight is approximately south of London, its railway has used tube trains since 1967. In the early 1960s it was proposed to close the island's whole railway network, but the route from to was kept as buses could not cope with the summer holiday traffic. Updating the system was necessary, but tunnels on the island required rolling stock lower than the standard main line stock. The line was electrified and forty-three cars of Standard Stock were purchased by British Rail, delivered in the spring of 1967 and ready for that summer season. These trains were replaced in 1989 by 1938 Stock, refurbished and formed into two-car Class 483 units. In January 2021 the 1938 Stock was withdrawn from service. The line is currently (as at May 2021) undergoing engineering works (including platform height raising) to allow more recent London Underground D78 Stock to operate. These heavily refurbished train sets are known of as British Rail Class 484 and (after some delays caused by software issues) entered service in November 2021. Inter-car barriers All London Underground rolling stock has recently been modified to include inter-car safety barriers between the cars. These were first fitted to the D78 Stock and 1973 Stock in late 1997 to prevent passengers from boarding trains from in between the cars and to prevent drunk people from falling between cars and being seriously injured. They were fitted to the rest of the rolling stock in 2000. Unfortunately, this meant the mounting of blisters on the front ends of the C Stock as well as the double ended A Stock, D Stock, 1967 Stock and 1973 Stock in the case that the cabs were coupled in the middle of a train.