Tunnel comparisons: length, depth and opening date, side by side

• 34entries listed

Every comparison

Each comparison is its own page with a permanent address, so a specific matchup can be linked to directly. Only structures open to traffic are compared.

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

How this table is compiled

This index lists 34 head-to-head comparisons, each on its own page with a permanent address. Transverse ventilation gives each section its own supply and extract, which is why the long two-lane crossings carry a false ceiling. Cost figures are excluded throughout this archive, because currency, inflation and differing project scope make them close to meaningless in comparison.

A boring machine has to be assembled underground and is economic only past a length that varies with the rock. Length stands in for terrain more than for difficulty, and on a head-to-head the two crossings rarely faced the same terrain. Ventilation arrangement caps how long a bore can be driven more directly than money does.

A tunnel's gradient is often the more interesting figure, particularly on subsea crossings where vehicles have to climb back out. The interesting figure on most crossings is the gradient or the cover, and neither appears in a ranking by length. Rock cover above the bore governs a subsea design, not the depth of water above that.

A tunnel outlives the traffic forecast that paid for it, and most of its lifetime cost is ventilation and lighting. Base tunnels replaced summit lines that climbed by spiral and switchback, and several of those older routes survive above them. The first long bores were driven by hand and gunpowder, and their alignments still show it.

Overburden at the deepest point sets the lining, and on a long crossing it varies more than the length suggests. Published lengths for the same structure differ by a few metres between sources, depending on whether cut-and-cover approaches are counted. The tail of a record is more representative of what gets built than its head is.

Reading the figures

Opening dates refer to the admission of traffic, not to breakthrough, which normally falls a year or two earlier. Two-way traffic in one bore is what modern regulation avoids and what most older road crossings were built with. Environmental consent now outlasts construction on many schemes, and the dates in a record rarely show it.

Wartime damage closed several crossings for years and a few were never reopened to their original use. This archive has held per-country and per-class tunnel inventories since the late 1990s, compiled from operator and administration sources. Lighting is brightest at a portal in daylight, because the adapting eye is the hazard rather than the dark.

Catenary needs headroom a road tunnel does not, so an electrified bore is taller for the same traffic. The oldest crossings still carrying traffic were built before any of the codes that now govern their upkeep. Traffic volumes are excluded for the same reason, and because they date far faster than the structures themselves.

Reconstruction after a fire is recorded because it usually changes both the profile and the ventilation arrangement. A comparison of two crossings is a comparison of two ground conditions, and the length column records neither. A short bore beneath a city can cost more than a long one through a mountain.

Height above sea level is a separate record from length. Both figures come from the same archive and the same convention. Sequential excavation is slower per metre and far more tolerant of ground that changes without warning. Cross-passage spacing, fixed firefighting and emergency ventilation control are what modern tunnel safety regulation actually governs.