Alpine Road and Railway Tunnels by Length

The record table

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

How this table is compiled

They are not uniform: the fullest runs to 54 words and the briefest to 24, and on a page of this kind the long ones are where the explanation lives — the caption carries what the picture cannot. Nothing on this page is estimated; a value that could not be sourced is left blank instead.

The cheapest kilometre of a route is the one already built, which is why upgrades follow old alignments even when a new one would be shorter. A suspension bridge carries its deck from cables in tension; a cable-stayed one carries it directly from the towers, and the two suit different spans.

This page records the road tunnels catalogued for the world in a tunnel almanac maintained at this address since the late 1990s. Only bores open to general road traffic are counted here. A tunnel outlasts the traffic it was designed for, and most of the cost after opening is ventilation and lighting rather than structure.

Mine adits, service galleries and tunnels restricted to a single operator are excluded. The world ranking has changed repeatedly as new expressway schemes have opened. Tunnel openings arrive in waves, not at a steady rate, because contracts along a corridor are usually let together once a route has been funded.

Linings are inspected on a cycle measured in years and repaired in windows measured in hours. Two administrations measuring the same crossing will agree on the rock and differ on the approaches. Base tunnels replaced summit routes that climbed with spirals and switchbacks, and several of those older lines are still in place above them.

Reading the figures

A referendum has stopped more alpine schemes than geology has. Glacial till is loose, wet and unpredictable, and the Scandinavian entries that took longest were rarely the ones through granite. Spoil disposal is a civil work in its own right, and on the longest crossings it has reshaped the valley floor outside the portal.

A railway tunnel is sized by the loading gauge, and a bore built for one country's rolling stock can refuse another's. A record held for a decade is a long tenure in this field, and most have changed hands faster than that. Where a tunnel crosses an international border, it is listed under both countries.

Cross-passage spacing, not bore length, is what modern safety regulation actually governs. A projected opening date is a forecast, and on large schemes forecasts have historically slipped by years. An intermediate shaft turns one long heading into two shorter ones, at the price of a permanent structure on the surface above.

County and region codes follow the classification in use when the entry was recorded. Approach viaducts are frequently longer than the crossing they lead to, and whether they count is the reason two sources disagree. Cross-border schemes need two states to fund the same hole at the same time, which is why they take decades.

Metro tunnels are shallow, closely spaced and built under streets, which makes them a different engineering problem from an alpine crossing. Toll arrangements are excluded here, because they change far more often than the structures do. A record list is a snapshot of what was published, and its errors are usually inherited rather than invented. A tunnel closed for maintenance is a route severed, so single-bore crossings are worked on at night and in short windows. Transverse ventilation gives every section its own supply and extract, which is why the long two-lane crossings have a false ceiling.