International Car Plate Codes and Their Countries: N to Zw

The record table

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

How this table is compiled

Escape and rescue provision has driven most of the change in tunnel design over the past three decades. Cost figures are omitted throughout, since currency, inflation and scope make them close to meaningless in comparison. The deepest point of a subsea tunnel is a sump, and its pumps run for the life of the crossing.

Two crossings of the same length built fifty years apart are different objects, and only the number is comparable. The oldest crossings still in service were built before any of the design codes that now govern their maintenance. Japan's rail network drove long-bore practice decades before its roads did, and its list reflects that order.

Dates before 1900 are frequently approximate, and are shown as published, unreconciled. The tail of a list is where the ordinary infrastructure sits, and it is more representative of what gets built than the head is. Ventilation type is recorded where known, because it constrains how long a bore can be built without intermediate shafts.

Trade press reporting is faster than official publication and less reliable, which is why an opening date sometimes moves after the event. Emergency lay-bys are spaced by regulation rather than by geometry, which is why they appear at intervals the alignment does not explain. A referendum has stopped more alpine schemes than geology has.

The note column is often the most useful part of a row, recording tube counts, gradients, closures and reconstruction dates. A tunnel boring machine produces a circular bore, which is why cross-section area and length do not scale together across entries. A record is a statement about what has been published, not about what exists.

Reading the figures

A railway tunnel is sized by the loading gauge, and a bore built for one country's rolling stock can refuse another's. Lighting at a portal is brightest in daylight, because the eye adapting from sun to bore is the hazard, not the darkness inside. Where a tunnel crosses an international border, it is listed under both countries.

Motorway tunnels are usually twinned, and the second bore is frequently built decades after the first. The first railway tunnels were driven by hand and gunpowder, and their alignments still carry the marks of both. Gradient inside a road tunnel is kept gentle for heavy vehicles, which lengthens the bore to gain the same height.

Tunnels built for one purpose are regularly repurposed for another, and a disused rail bore is the commonest cycleway in some countries. Rock cover above a subsea bore is the governing design constraint, not the depth of the water itself. Round numbers in an old list are usually estimates that hardened into record over time.

Water under pressure is the single most disruptive thing a heading can meet, and it is rarely where the survey said it would be. Comparing two national lists says as much about how each country records its infrastructure as about the infrastructure itself. Shotcrete applied at the face turned temporary support into permanent lining and changed what lengths were buildable.

The interesting figure on most crossings is the gradient or the cover, and neither appears in a length ranking. Reconstruction after a fire changes the ventilation and the escape arrangement, and often the recorded length as well. Environmental consent now takes longer than construction on many schemes, and the dates in a list rarely show it.