The initial system had a relatively low capacity, but the Docklands area very quickly developed into a major financial centre and employment zone, increasing traffic. In particular Tower Gateway, at the edge of the City of London, attracted criticism for its poor connections, as it did not connect directly with the nearby Tower Hill tube station or Fenchurch Street railway station. The criticism arose partly because the system usage was higher than expected. Plans were developed, before the system opened, to extend it to in the west and Beckton in the east. Stations and trains were extended to two-unit length, and the system was expanded into the heart of the City of London to through a tunnel, which opened in 1991. This extension left on a stub. The original trains were not suitable for underground usage due to not meeting the fire safety laws for underground trains. They were operated for a time on the above-ground sections only, and were later sold.