In 1984 the first serious proposal for construction of a subway appeared in the Municipal People's Congress. In April 1986, the Nanjing Integrated Transport Planning group was established to research on how to implement a subway system in Nanjing. In December 1986 the team published the "Nanjing Metro Initial Phase". The phase consists of a north–south line, east–west line and a diagonal Northwest to Southeast line. The three lines meet in the city center forming a triangle. A revision of the "Nanjing City Master Plan" in 1993 added another line through the urban core, and three light metro lines connecting Nanjing's suburbs in Pukou and the at time proposed new airport. In addition a suburban railway to Longtan was proposed. A 1999 report on "Nanjing city rapid rail transit network planning" further proposed six subway lines, two subway extensions and three light metro lines.