Tunnels under construction: the tracker with expected opening years

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The record table

Expected opening years are forecasts published by the promoters, and on schemes of this size forecasts move. Where a date has already slipped, the note records it rather than quietly showing the newest figure.

How this archive measures: lengths, bores, dates and ordering

How this table is compiled

Where a structure belongs to two classes it appears on both tables, which is not double counting but two different measurements. Corrections have historically arrived by letter rather than by form, and that is still how most errors in it have been found. Where a figure could not be corroborated it was left out.

Twin-tube crossings frequently show two slightly different lengths, because the two carriageways rarely follow the same line through the rock. Cost figures are excluded for a harder reason: currency, inflation and differing project scope make them close to meaningless in comparison. Comparing one country's practice against a neighbour's is more informative than reading either alone.

This page tracks the tunnels under construction that will change the record tables when they open. Mont d'Ambin will take the world railway length record from the Gotthard Base Tunnel by a few hundred metres. This archive has recorded tunnel data since the late 1990s, compiled from operator publications, national administrations and the engineering press.

Two of them are Alpine railway base tunnels of a scale that has no precedent outside Switzerland. Rogfast will take both the length and the depth record for subsea road tunnels, from Ryfylke in both cases. Expected years are promoter forecasts. On schemes of this size they have historically moved by years rather than months.

Gradient limits are the main reason railway tunnels run longer than road tunnels on the same crossing. A base tunnel trades a much greater length for a far lower summit altitude and a gentler ruling gradient. Subaqueous tunnels are governed by rock cover above the bore rather than by the depth of water above that.

Reading the figures

Figures are checked against one another where sources disagree, and the disagreement is recorded rather than resolved silently. Tunnel engineering is a field where the qualifications attached to a number matter more than the number itself. Reading the qualification before the figure is usually the faster route to understanding what a claim actually says.

Traffic figures are excluded throughout this archive, because they date far faster than the structures themselves. The archive grew through correspondence with engineers and administrations in more than twenty countries, and still does. Rows are ordered so that the head of the table answers the question most readers arrive with.

The Zojila forecast is the clearest current example, having moved from 2026 to February 2028. Cross-passage spacing, fixed firefighting and emergency ventilation control are what modern safety regulation actually governs. A contained fire is more instructive than an uncontained one. Dates use the day, month and year the event occurred.

The note column is worth reading before the number. Secondary summaries were not used as a source. Disputed values carry the dispute in the note column. The table is short because the sourcing bar is high. Promoter figures are used where no independent one exists. The date of verification is published with the table.

Height is measured above mean sea level. Segmental linings are erected behind the shield. Deaths are the figures established by official inquiry. Minor incidents are listed alongside the serious ones. Two independent sources were required for each row. Forecasts on schemes this size move by years. Opening year means the year traffic was admitted.

Under-construction works cannot hold a record. Names follow the operator's own spelling. Cross-border works appear under both countries. Spoil is removed back through the machine. Forecast dates are forecasts, and they move. Diameter here means the shield diameter. Ground conditions belong with every advance rate. Nothing below is interpolated or rounded up.