Beijing traffic police have started using robots to catch drivers who park illegally on a major highway.

Three devices that look like small suitcases have been fitted to guardrails along the Jichang Expressway, which runs 18 km from downtown to Beijing Capital International Airport.

The "robocops" weigh 20 kg and patrol up and down the rails, traveling at up to 5 km/h, according to the Beijing Traffic Management Bureau.

Each is equipped with a 360-degree camera for taking pictures of vehicles parked in the emergency lane. These images will automatically be sent to traffic police officers via an app.

Guo Wei, an officer with the bureau, said illegal parking on highways has been a problem for a long time, especially near the airport. Not only does it cause congestion, but it also threatens safety, he said.

The devices went on trial on Oct 3. So far, they have been reporting 50 offenses a day, Wang Zhenshan, vice-captain of the Chaoyang traffic police detachment, told Beijing Youth Daily.

Shaoxing, a city in Zhejiang province, also tried out a similar system — and recorded 20 offenses in just the first hour, the local traffic police said on Sina Weibo.

Last year, 1.3 million cases of illegal parking in emergency lanes were reported nationwide, up by 92 percent year-on-year, according to the Ministry of Public Security’s Traffic Management Bureau.

If the robots perform well during the trial, the program is expected to be expanded to more highways.