In 2002, construction of the Circle Line, which was previously conceived as separate LRT lines, commenced and was to connect the sub-regional centres of Bishan, Paya Lebar and Buona Vista together. However, construction was impeded by the collapse of Nicoll Highway in 2004 that claimed four lives and injured another three. Operations of the fully automated medium capacity line only commenced in 2009 and the original line was fully completed by 2012. The second medium-capacity MRT line, the Downtown MRT line, was built from 2008 and was opened in stages from 2013 to 2017. In January 2020, the sixth MRT line, the Thomson-East Coast MRT Line, commenced operations.