Youngest Tube -

For a moment between 2021 and 2023, the title of "youngest tube" belonged to the Moscow Metro’s Bolshaya Koltsevaya line (Big Circle Line). When President Putin inaugurated the final section in March 2023, it became the world’s longest circular metro line (70 km).

However, by 2025, Moscow’s line is no longer the "youngest" because newer segments in Paris and China have opened since then. Yet, it remains a benchmark for how fast a "young tube" can be built—using 150 tunnel boring machines simultaneously.

When urban planners and transit enthusiasts talk about subway systems, the conversation often revolves around the oldest lines—the London Underground’s Metropolitan line (opened 1863), the Budapest Metro, or the Glasgow Subway. However, there is a growing fascination at the opposite end of the spectrum: the "youngest tube."

The term "youngest tube" refers to the most recently opened fully automated, high-frequency metro line that operates underground in a major metropolitan area. While the title changes hands every few years as cities like Moscow, Delhi, and Paris inaugurate new segments, one name consistently dominates the conversation as of 2025-2026: Line 14 of the Grand Paris Express. youngest tube

But what qualifies a line as the "youngest tube"? Is it simply the newest extension, or does it require a completely new route, rolling stock, and signaling system? This article explores the engineering marvels, the cities competing for the title, and why transit authorities are racing to build these modern arteries.

There are four useful interpretations:

Each lens reveals different technological, social, and design priorities. For a moment between 2021 and 2023, the

The title is fleeting. Here are the projects that will steal the crown in the next 18 months:

Not every “tube” needs long, heavy trains. Small-scale systems suit low-density corridors, tourist zones, campuses, and historic city centers where big infrastructure is infeasible.

Notable types:

Design advantages of small-scale tubes:

Trade-offs: