Subaqueous Road Tunnels: Subsea Bores and Immersed Tubes by Depth

• 83entries listed
• 14.46 kmlongest bore
• 1927–2023openings span
• 355.85 kmtotal length

The subaqueous road tunnels, ranked by length

Figures on this page were last checked against operator and administration sources on 2 September 2026.

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

Subsea bores, rock cover and gradient

The entries sum to roughly 355.85 km of bore, an average of about 4.39 km each, though that average describes no actual row. The middle half of the table runs from 2.61 km to 5.71 km, and that band is where most of the engineering on this page actually sits.

The shortest recorded entry is 2.01 km against 14.46 km at the top, a spread of 7.19x across the same table. The three longest entries alone account for 37.7 km of the 355.85 km on this page, which is 11 per cent of the total from 3 of 81 rows.

Between the longest and the tenth-longest the drop is 6.72 km, which is the part of the table that changes when a single scheme opens. Where one of these 81 lengths disagrees with an operator's own figure for the world, the table keeps the published value and notes the difference instead of averaging the two.

Roughly 37 of the dated entries opened in this century, which is a rough measure of how much of the network is recent. Lengths for the world are recorded in metres which is how the operators publish them and why the shortest entry here reads as 2 012 m and not a rounded figure.

The longest stands 2.46 km clear of the next longest, which is the margin to watch when a new scheme is announced. A new scheme in the world would have to beat 14.46 km to change the head of this table, and that is the figure worth rechecking when one opens.

Immersed tubes versus bored rock tunnels

The 81 rows for the world are ordered by length, not by date, so the 2023 opening sits well down the table without being any less current. The longest entry is 7.2 times the shortest and 4.3 times the median, which is the quickest measure of how uneven the table is.

Where a figure could not be sourced the cell is left blank, so what is shown is measured and nothing is inferred. Sorting on that one dimension is imperfect, since geology decides difficulty, but it is the measure published consistently enough to rank on. Immersed tube construction suits short, shallow crossings where boring would be uneconomic.

36 of the 81 entries fall within a quarter of the median length, which is how tightly this particular list clusters around its typical structure. 13 of the dated entries opened from 2010 onwards, which shows how much of what is listed here is recent construction and not historic work.

The shorter half of the table totals 105.56 km against 250.3 km for the longer half, from the same number of rows. Eighth on the list is Bømlafjord at 7.93 km, which is where the table stops being about record holders and starts being about ordinary infrastructure.

Depth below sea level as a design constraint

After the 2000s the next busiest decade here is the 1990s with 18 openings, so the building effort came in more than one wave. The dated entries fall across 43 different years, which is a rough measure of whether this was a sustained programme or a handful of separate schemes.

40 entries sit above the median and 41 at or below it, so the table is top-heavy and not clustered at one end. The ten longest average 9.83 km against 3.63 km for everything below them, and that ratio is the clearest thing this table says about the distribution.

Reading a list of subaqueous road tunnels

This page records the road tunnels catalogued for the world in a tunnel almanac maintained at this address since the late 1990s. Laid end to end the entries on this page would run 355.85 km, which is a number with no engineering meaning but a useful sense of the scale of what is catalogued.

Treat the table as the argument and the prose as the footnote: the numbers carry the case. Read down the length column, the 77 values run from 2 012 m to 26 700 m with a midpoint at 3 400 m; the spread rather than the maximum is what says how uneven this set is.

Depth below sea level is recorded where it is published, because it drives the gradient. 76 of the 77 rows carry an entry in the notes column — 99 per cent of the table — and that column is where the qualifications live: tube counts, closures, boundaries and the reason a figure reads the way it does.

Further down the table, Sandoy is recorded at 10.8 km and Tokyo Aqua at 9.58 km. The material on this page is held in 59 captions rather than in running text, 495 words of it, each written against the image or row it belongs to by the compiler who put the page together.

Dated entries run from 1927 to 2023, and the busiest decade is the 2000s with 24 recorded openings. They are not uniform: the fullest runs to 21 words and the briefest to 6, and on a page of this kind the long ones are where the explanation lives — the caption carries what the picture cannot.

Dates for the world refer to opening to traffic, not breakthrough, so the 1927 entry was under construction for some years before that. The captions name 63 distinct places and structures — River, Stavanger and Bergen among them — and those names are the index into the length tables where each is recorded with its own figure.

The table on this page runs to 77 rows and records Country, Tunnel, Length, Date of opening and Notes for each of them, which is the shape the original compiler chose rather than one imposed here. Compressed-air working let shafts be sunk through water-bearing ground and cost the health of the men who did it.

2 of those 83 are recorded as under construction or planned, the longest of them Rogfast at 26.7 km, so the count includes them while every measured figure — the range, the median, the total — describes the 81 rows carrying traffic today: an unopened bore cannot hold a record. Only bores open to general road traffic are counted here.

The 2000s account for 24 openings here and the 1990s for 18, so the building effort was not spread evenly across the period. The tunnel column names 77 distinct entries on this page, Ryfylke and Eysturoy among them, each traceable to the operator or administration record it was taken from.

What follows is a list of subaqueous road tunnels and not a selection, with every row traceable to a published source. Subsea bores run beneath a fjord or strait with rock cover, not water, above the lining. The dated entries carry 43 distinct opening years across 96 years, and the median opening year is 1999.

Subsea tunnels are pumped continuously, and their low point sits well below sea level. An immersed tube is prefabricated in sections and sunk into a dredged trench. Only Ryfylke sits within ten per cent of the longest figure, so one structure stands 2.46 km clear of the field here.

Depth, not length, is the governing design constraint on most subaqueous crossings. Nothing in this table is estimated: where a value could not be sourced it is left blank. 25 of the 81 measured entries exceed five kilometres, and those are the ones that carry a full ventilation and escape regime.

Anyone comparing these figures across borders should read the note column too, since national practice varies. The longest entry is Ryfylke, at 14.46 km, opened in 2019. 4 entries reach ten kilometres and 0 reach twenty, a distribution that decides how much of this table needs full mechanical ventilation.

Second and third place go to Ryfylke at 14.46 km and Sandoy at 12 km. Openings average one every 1.3 years across the dated entries here, though they arrive in clusters, not at that rate. The earliest dated entry is Tokyo Aqua, opened in 1997, and the most recent is Sandoy in 2023.

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. Box girders replaced trusses on medium spans because they are stiffer in torsion and cheaper to maintain. Dates before 1900 are frequently approximate, and are shown as published, unreconciled.