How a Tokyo subway line was built to prevent a repeat of tragedy

Society · Published 9 October 2026 Swipe more like this →

In short: The Chiyoda Line was not merely designed to alleviate congestion in central Tokyo. Its construction was an urgent priority to relieve the Jōban Line, which had reached a breaking point. This overcrowding was a critical factor behind the conditions that led to the devastating Mikawashima train crash in the 1960s.

The Chiyoda Line, officially designated as Line 9, was conceived in the 1960s to address severe capacity issues on existing rail infrastructure. Initially proposed in 1962 under Urban Transportation Council Report No. 6, the project was fast-tracked to provide a bypass for the Hibiya and Ginza lines. Beyond simple efficiency, the line served a vital safety function: reducing the extreme overcrowding on the Jōban Line, which had contributed to the circumstances surrounding the Mikawashima train crash. By the time construction began in July 1966, the necessity of the line was clear, and it was prioritized over other planned routes like the Namboku and Yūrakuchō lines.

The line's development involved complex negotiations regarding its route and integration. While early plans suggested a branch from the Odakyu Line at Kitami, operational conflicts led to the current configuration where services diverge at Yoyogi-Uehara. The line officially finalized its 32.5 km route between Kitami and Ayase in December 1964. The name itself was chosen through a democratic process: the Teito Rapid Transit Authority held an employee competition, and 'Chiyoda' received the most votes, beating out alternatives like 'Otemachi Line'.

Today, the Chiyoda Line is a critical artery for Tokyo, carrying over 1.4 million passengers daily. It is known for its extensive through-running services, connecting to the JR East Jōban Line in the northeast and the Odakyu Odawara Line in the southwest. The line has also pioneered unique services, such as the Odakyu Romancecar limited express, which introduced reserved-seating to the subway network in 2008. Despite its success, the line has faced significant challenges, including the 1995 Aum sarin gas attack and the extreme congestion that reached 181% of capacity in 2009, though rates dropped to 139% during the COVID-19 pandemic.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Tokyo's busiest subway line was a century-long struggle to connect east and west
• The Tokyo railway line that was never intended to carry a single passenger
• How Tokyo’s subway evolved from a failed 1906 proposal into a massive public company.
• The Keihin–Tōhoku Line: A Vital Artery Connecting Tokyo, Yokohama, and Saitama's Urban Centers
• How Nagoya’s Rapid Transit System Evolved From Wartime Planning to a Modern Circular Network
• From German colonial workshops to high-speed rail, a century of locomotive evolution
• The CRH2 train series transformed China's high-speed rail from imported technology to domestic innovation.
• How a single driver revolutionized the efficiency of modern rail travel
• How a Spanish train platform became the backbone of regional rail across the globe
• The engineering paradox of the railway break-of-gauge
• The locomotive that redefined visibility and dominated North American rails for decades
• How a single train design reshaped Tokyo's complex commuter networks

More in Railways · More in Society · Latest · A–Z · All topics