Stations to the east of the 3rd Ring Road to Tongzhou are more widely spaced, the furthest being 4 km (2.5 mi) apart.

Though due to its alignment through some of Beijing's densest residential neighborhoods and paralleling the overcapacity and busy Line 1, some industry leaders believed that the average daily passenger flow of the line may reach 1.4 million passengers per day sooner than expected.

Authorities responded by adding more trains and shortening headway to reduce crowding on the line.

However, this alignment would make the central section of Line 6 tunnel extremely close to the Forbidden City.

[15] Line 6 in Phase I was originally slated to have elevated tracks for 7 km (4.3 mi), east of the 5th Ring Road, from Dingfuzhuang and Changying.

After residents along the route raised concerns about train noise, planners reconsidered and ultimately decided to keep all of Phase I underground.

[30] In Phase II, which opened in 2014, Line 6 was extended further east by about 12.8 km (8.0 mi) through six stations from Caofang to Lucheng in Tongzhou District.

[31] However, due to a shortage of rolling stock, express services have yet to be implemented when the Phase II opens in 2014.

In 2018, the government announced that sufficient rolling stock had arrived to begin implementing an express service.

In 2011, because of issues of low capacity and electromagnetic radiation concerns of Maglev technology, city planning authorities proposed to detach several stations from Line S1.

This would extend Line 6 for 10.556 km (6.559 mi)[34] west with six stations from Jin'anqiao to Haidian Wuluju (the western terminus of Phase I).

[37] The revision was formalized and submitted to the National Development and Reform Commission for review in March 2012.