At first, an articulated type of rolling stock was thought about. This idea was not used because it would have been too hard to move the stock to Acton Works for heavy overhauls. This is no longer a problem since train overhauls have been moved away from Acton Works to the builders' own works. The new 2009 tube stock is wider and the carriage is slightly longer. This means it can only run on the Victoria line, as it is too wide for the tunnels of other deep level tube lines.