Chongqing Metro Line 2

Chongqing, China

Escalators, Modernization

Introduction

Otis modernized 119 elevators and escalators on the high-traffic Chongqing, China Metro Line 2 — all without disrupting passengers. The project took more than 30 months to complete and was finalized in June 2023. It is currently the largest modernization project conducted by Otis in China.

Chongqing Metro Line 2 opened in 2005 as the first urban rail transit line in western China and the first straddle monorail line in China. It has 18 stations and includes underground sections, elevated sections and even a station between the sixth and eighth floors of a residential building. It is one of the world’s busiest monorail lines, carrying more than 1 billion passengers to date, and is key to the unique transportation network in this densely populated and mountainous city.

Otis has provided more than 560 units of elevator and escalator equipment and professional maintenance services for the Chongqing Metro on lines 2, 9 and 10. 

Project Description

The project included replacing 16 existing escalators and upgrading them to Otis 515 NPE escalators, as well as existing-truss modernization for 85 escalators ranging from 3.5 to 13.5 m. None of the original escalators were installed by Otis; they came from various manufacturers. Existing-truss modernization retains the existing escalator framework, repairs it to a high-quality standard as necessary and updates it with new equipment, minimizing downtime and disruption. The end result improves ride quality and the passenger experience.

The modernization project further enhanced the escalators’ safety and performance. The maximum running speed of the escalators increased by 30%, from 0.5 to 0.65 m/s, and the modernized escalators are equipped with a variable frequency function, in which running speed is automatically adjusted based on changes in passenger flow, moving passengers more quickly when needed and reducing unnecessary energy use between crowds. 

The existing-truss modernization technique meant the new escalator components could be assembled in the factory and delivered and installed directly on-site, with significantly less disruption to the metro’s daily operations. 

Otis also modernized 16 Gen2^® elevators and replaced two freight elevators. The modernized elevators feature ReGen™ drives and the Otis ONE^® Internet of Things (IoT) platform for real-time monitoring and predictive maintenance. Otis service professionals use an Otis smartphone app to identify problems, manage equipment and spare parts remotely to prevent service interruptions throughout the units’ lifetime. The accompanying Otis customer service CX app is a new digital technology that provides Chongqing Metro managers transparent access to their elevator data for improved elevator management like scheduling maintenance work, accessing operational records and commercial services and running elevator health checks. 

The Transportation System: Meeting the Challenges

The existing-truss escalator modernization method provided great advantages to this project, but there were still technical challenges and complexities that needed to be overcome.

First, the truss dimensions — needed for accurate assembly of the new components — could only be obtained once the original escalator was dismantled. 

Otis made detailed measurements of the truss dimensions to minimize disruption to the original truss support structure. Based on the measurement data, Otis modeled each escalator and customized the interface to match the existing support structure.

Senior engineers formulated a retrofit process and any tooling needed, paying close attention to specific requirements from the construction site, and applied quality control methods from the factory to the existing-truss retrofit. 

Responding quickly to jobsite needs, the factory team leveraged a phased design and manufacturing method and worked closely with the supply chain to meet the needs of the on-site installation teams during each phase of work. Specifically, the factory arranged for workshop fitters to join each installation team at the construction site to provide specialist support.

Accuracy, close collaboration, effective communication and pace were all essential to maintain progress and minimize downtime once the modernization work started.

Second, as existing-truss modernization depends on the re-use of existing-trusses, it was critical to demonstrate their integrity and safety. Otis formulated truss evaluation processes, including truss strength analysis, surface treatment inspection and weld seam inspection, and conducted any required truss strengthening.

Third, truss width was limited, and, in many cases the existing trusses were too narrow for the new main drives to fit through. Otis engineers developed an optimized structure for the drives and developed a new lifting solution to safely and effectively place them without having to remove or re-engineer the truss. The full Otis team collaborating on this included specialists in Sales, Design, Major Project Management, Quality Management, Procurement and Field.

Other challenges were specific to the unique nature of the project sites and Chongqing itself.

Otis’ primary objective was to execute the modernization project without disrupting routine train services. This 30-month project was coupled with a tight construction timeline (which was impacted by the global pandemic) and a demanding workload. Most work had to be performed overnight from midnight to 5 a.m. Chongqing’s mountainous geography meant that much of the equipment could only be transported to worksites using manpower and an equipment-lifting tool. 

Work was done in alignment with station renovations and required an efficient way to remove the old escalator and replace it with a new unit, including careful planning of shipments to match the specific lifting height for each station. 

The complex construction environment included other challenges, as well. Because of the city’s unique geography, station design varied greatly, and the project included cantilever, floor standing, stacked and underground shaft types. Each escalator had a unique construction plan according to its environment and location, with the aim of putting safety first. Each plan required customer confirmation before work started.

Finally, there was a wide range of equipment to modernize: More than 100 of the combined elevator and escalator units were manufactured by a company other than Otis, including international manufacturers and one local company. These units had different specifications and often differed from current product lines — adding complexity because each piece of equipment had to be evaluated to execute the modernization with minimum disruption. 

Conclusion

Otis China has played an important role in the urban renewal of Chongqing, and our work on Metro Line 2 is an important part of it. We’re proud of our efforts to keep the metro’s 4 million daily passengers moving smoothly and safely through the network.