An algorithm schedules and manages the nightly engineering work on one of the world's best subway systems – and does it more efficiently than any human could

Who’s in charge? Bloomberg/Getty

JUST after midnight, the last subway car slips into its sidings in Hong Kong and an army of engineers goes to work. In a typical week, 10,000 people carry out 2600 engineering works across the system – from grinding rough rails smooth and replacing tracks to checking for damage. People might do the work, but they don’t choose what needs doing. Instead, each task is scheduled and managed by artificial intelligence.

Hong Kong has one of the world’s best subway systems. It has a 99.9 per cent on time record – far better than London Underground or New York’s subway. It is owned and run by MTR Corporation, which also runs systems in Stockholm, Melbourne, London and Beijing. MTR is now planning to roll out its AI overseer to the other networks it manages.

“It will probably be Beijing first,” says Andy Chun of Hong Kong’s City University, who designed the AI system and worked with MTR to build it into their systems. “Before AI, they would have a planning session with experts from five or six different areas,” he says. “It was pretty chaotic. Now they just reveal the plan on a huge screen.”


Chun’s AI program works with a simulated model of the entire system to find the best schedule for necessary engineering works. From its omniscient view it can see chances to combine work and share resources that no human could.

“We asked the experts what they consider when making a decision, then formulated that into code”

The schedule generated is still subject to human approval. Urgent, unexpected repairs can be added manually – the system simply reschedules less important tasks.

It also checks the maintenance it plans for compliance with local regulations. Chun’s team encoded into machine readable language 200 rules that the engineers must follow when working at night, such as keeping noise below a certain level in residential areas.

The AI overseer saves MTR two days a week of wrangling over the repair schedule. Also, MTR’s repair teams now have 30 minutes longer to finish their night’s work – a small time boost that saves MTR $800,000 a year.

The main difference between normal software and Hong Kong’s AI is that it contains human knowledge that takes years to acquire through experience, says Chun. “We asked the experts what they consider when making a decision, then formulated that into rules – we basically extracted expertise from different areas about engineering works,” he says.

Adel Sadek, a transport engineer at the University of Buffalo in New York, says Hong Kong’s system shows the power that niche artificial intelligence can have, as opposed to the dream of a human-level intelligence.

AIs like Chun’s do face a problem. His team spent months finding the most efficient algorithm for designing schedules. It settled on a genetic algorithm, which pits many solutions to the same problem against each other to find the best one. But the people that had to carry out the scheduled work took a while to get used to the idea, as they didn’t like not knowing why they were doing certain things.

Sadek says similar problems crop up when trying to get transport departments in the US to use AI to improve their networks. “People get scared when you talk to them about AI,” he says. “A Department of Transport official is responsible for lives, they want to see how the decisions are being made.”

Visa approved, human It’s not just subways in Hong Kong that are seeing the benefits of artificial intelligence (see main story). Every application for a visa, passport or residency that goes through Hong Kong’s Immigration Department is looked over by AI. Software sorts the applications into those that are clearly approved, clearly denied and in a grey area. People still have the final word on each application, but the algorithm does much of the heavy lifting. To help the software work, the rules and laws governing entrance documents for Hong Kong were converted into a machine readable language. “A huge chunk of the application is looking for compliance with regulation,” says Andy Chun of Hong Kong’s City University, who created the algorithm. “What our AI decides is which cases are easy, and which require more human input.”

This article appeared in print under the headline “The subway run by AI”

Read: “A new wave of tech will test our automatic faith in machines“

When this article was first published, Andy Chun's name was misspelled