The Daxing Airport Express was originally planned to start from Mudanyuan, and be routed in parallel with
Line 19 from Mudanyuan to Caoqiao. However, the plan would cost more than 40 billion yuan, which was considered too expensive for a dedicated line that would only serve passengers going to and from the airport. The parallel section with Line 19 was abandoned and the route was shortened to the stretch from Caoqiao to Daxing Airport. The investment required for the line was reduced by 20 billion yuan. and a plan with 4 stations: Caoqiao, Daxing Xincheng, and two stations at the Daxing Airport. In early 2016, it was announced that the Daxing Airport Express was slated for completion by 2019. Phase I of the line includes only 3 stations: Caoqiao, Daxing Xincheng and Daxing Airport. The line will operate at a top speed of using Type D Construction started at the end of 2016. Test runs on the line began in June 2019, and the line was opened on September 26, 2019 (Phase 1). ==Future expansion==