A malfunctioning automatic stopping system caused the recent collision of two underground trains in Seoul, officials say.
A moving train slammed into the rear of another, which had stopped at Sangwangsimni station in eastern Seoul on mid-afternoon on Friday, leaving more than 200 people injured.
One elderly woman was seriously hurt, while more than 150 required some sort of treatment - mainly for cuts and sprains.
The accident was a fresh blow to a country still reeling from the April 16 Sewol ferry tragedy that left 300 dead or missing - most of them high school students - after the ship capsized and sank.
"The Automatic Train Stop system (ATS) installed at Sangwangsimni station failed to function properly", Seoul Metro President Chang Jung-woo told journalists.
ATS is designed to control the distance between trains, and should activate when the two trains were within 200 metres of each other.
The system malfunctioned, consequently, the following train came too close to the stationary train, leaving little time for the driver to brake.
The tunnel curves before entering Sangwangsimni station and the driver did not see the platform was occupied until quite late, Chang added.
The last two carriages of the stationary train appeared to have been thrown off the rails by the force of the impact, and TV footage showed cracked windows on the two trains and one door connecting two carriages that had been completely knocked off its hinges.
Train service on the line No.2 returned to normal early Saturday.
Seoul's underground network is one of the busiest in the world, carrying about 5.25 million passengers a day, according to official data from City Hall.
The collision added to public anger and frustration with the country's lax safety standards exposed by the ferry disaster.
The Chosun Ilbo daily, with the country's largest circulation, said Saturday that Seoul underground line No.2 was built 34 years ago and was run down, and warned South Korea was not investing enough in maintaining its infrastructure.
"This country, however, has been parsimonious in investing in safety measures while rushing for ostensible economic achievement", it said in an editorial.
