The country’s most crowded subway line touched off outcry from passengers Monday, when the speed of all trains was slowed as a safety measure.

The Seoul Metro Line No. 2 was stalled during rush hour on the first day of the work week, with each train stopping at one station for as long as seven minutes or more.

“The delay in operation was caused by the rush hour crowd and trying to secure and maintain a safe distance between trains,” Seoul Metro wrote on its Twitter account. It also explained that the lag was not caused by any defect or malfunction in the trains.

Meanwhile, the passengers were only told through the intercom that the distance between trains was being adjusted, and given no clear instructions.

“It took me about 50, 55 minutes to get from Jamsillaru Station to City Hall Station,” said an office worker, who was 20 minutes late to work. “It usually takes me about 30 minutes. Why did they have to stall the trains when everyone was heading to work?”

In response to the protests from passengers on Line No. 2, Seoul Metro made a document available via its Facebook account to help employers check the delays. The document shows how long each train was delayed.

“We can’t say whether this will happen again,” a Seoul Metro official told The Korea Herald. “We’re not planning on taking any special action in response to the incident.”

By Suh Ye-seul (sys@heraldcorp.com)