Chongqing - Chongqing reached a new milestone in urban rail transit on December 20 as the first three-car train arrived at the Lujiao depot for Line 24, the city’s first fully automated metro line, enabling more flexible capacity to match passenger demand.

On December 20, Chongqing's first three-car train for the rail transit line 24 arrived at the Lujiao depot. (Photo/Chongqing Rail Transit)

What sets the train apart is its "3+3" flexible configuration, a first in China's urban rail sector. During off-peak hours, the train can run as a compact three-car set. When passenger volumes rise, two sets can automatically couple to form a six-car train without changing door spacing. This allows the line to respond quickly to shifting travel patterns while maintaining station operations and passenger flow.

The three-car train is 60 metres long and follows the overall design language of the line's six-car fleet. Its silver exterior is highlighted by orange and black accents that reflect the line's identity, giving the train a clean, modern look. 

Inside, the focus is on comfort and efficiency. The cars feature adaptive energy-saving lighting, ergonomic handholds, a draft-free air distribution system, and intelligent climate control. High-definition information screens and transparent partitions designed to simulate a driver's forward view create a more open, user-friendly cabin environment.

Behind the streamlined design lies a series of engineering firsts. To ensure that three-car and six-car trains can operate on the same line and couple seamlessly, engineers redesigned the car layout so that end cars and intermediate cars are the same length. 

This required shortening the cab section and developing new energy-absorption solutions to maintain safety standards despite the reduced coupling distance. Also, communication systems were upgraded so that train sets can exchange data instantly during coupling and decoupling, a critical requirement for fully automated operation.

Chongqing's line 24 is designed to dynamically adjust capacity by mixing three-car and six-car trains based on demand. (Photo/Chongqing Rail Transit)

Moreover, the trains are equipped with advanced safety and control systems. Active and passive obstacle detection, along with derailment monitoring, form multiple layers of protection. A digital logic control unit that meets the highest international safety standards replaces traditional relay-based systems, improving reliability and reducing maintenance requirements. 

After arriving at the depot, the first three-car train will undergo extensive testing. Engineers will check everything from traction and braking to air conditioning and passenger information systems. The train will also be tested in coordination with signalling, power supply, communications, and station systems to fine-tune fully automated operations before passenger service begins.

As a Grade of Automation 4 (GoA4) fully automated line, Chongqing's line 24 is designed to dynamically adjust capacity by mixing three-car and six-car trains to meet demand. This approach will improve efficiency, reduce operating costs, and better balance passenger flows across the network.