International Car Plate Codes and Their Countries: A to Mya

The record table

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

How this table is compiled

The cont column sorts these 53 rows into 6 groups, the largest being EU with 23, then AS with 16 and AF with 9. Switzerland's crossings are alpine and its practice is conservative, which shows in how few of its entries have ever been rebuilt. Corrections have historically arrived by letter from engineers and administrations in more than twenty countries.

Bridge and tunnel appear on the same route more often than either appears alone, because the terrain that requires one usually requires the other. Squeezing ground closes on a bore faster than it can be lined, and it is the condition that has delayed more alpine schemes than any other.

A national administration publishes what it maintains, so a crossing that changes owner can vanish from one list and appear in another. Toll revenue on a fixed link is usually pledged against the debt that built it, and the toll ends when the debt does. The Faroese crossings connect islands that had no fixed link at all within living memory.

A tunnel closed for maintenance is a route severed, so single-bore crossings are worked on at night and in short windows. Portals weather faster than the bore behind them, being the only part exposed to frost and sun. A projected opening date is a forecast, and on large schemes forecasts have historically slipped by years.

Water management is the maintenance problem that never ends, and drainage design decides how expensive it will be. Austria's north-south routes cross the main alpine chain three times, and its tunnel list is essentially that geography written down. Nothing on this page is estimated; a value that could not be sourced is left blank instead.

Reading the figures

A disused tunnel is expensive to fill and cheap to seal, which is why so many survive behind a wall. A tunnel outlasts the traffic it was designed for, and most of the cost after opening is ventilation and lighting rather than structure. Subsea tunnels are usually built with a low point well below sea level and pumped continuously.

A record list is a snapshot of what was published, and its errors are usually inherited rather than invented. Wartime damage closed several crossings for years, and a few were never reopened to their original use. The most useful sources are the least accessible: annual reports, inspection records and commissioning documents rather than press releases.

Metro tunnels are shallow, closely spaced and built under streets, which makes them a different engineering problem from an alpine crossing. A tunnel boring machine is economic only past a certain length, below which the cost of assembling it is never recovered. Toll plazas sit outside portals rather than inside them, for ventilation reasons as much as for traffic ones.

Seismic risk changes the lining rather than the alignment: a tunnel is among the safer places to be in an earthquake. Tidal range decides how deep an estuary crossing must sit, and it varies more between estuaries than the crossings themselves do. Aerodynamic pressure waves in a long rail bore are severe enough to need relief shafts or sealed carriages.

Water ingress is pumped out continuously on a subaqueous crossing, and the pumps are the one system that can never be off. An avalanche gallery is not a tunnel in the usual sense: it is a roof over a road, open on one side. A base tunnel trades a much greater length for a far lower summit altitude and a gentler ruling gradient.