Tokyo Aqua vs Changxing: length, opening date and class compared

• 5entries listed

Side by side

Tokyo Aqua is recorded on data/subsea.html and Changxing on data/subsea.html, compiled to the same convention, which is what makes the two figures comparable at all.

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

How this table is compiled

Neither holds the record: Sandoy at 10.8 km is the longest subaqueous tunnel recorded here, 1.22 km ahead of Tokyo Aqua. Both rows are reachable from the subaqueous tunnel table they were taken from, where the note column carries the tube count, the gradient and any reconstruction Tokyo Aqua or Changxing has had.

This archive separates 4 classes of structure and both entries here are indexed under subaqueous tunnel, which decides the table each is ranked in and the convention its length was measured by. Spoil from a long bore is a civil work of its own, and outside several alpine portals it has become a permanent landform.

That gap is about 7 per cent of the longer bore, which is the figure worth holding on to rather than the raw metres. Driven end to end the two would run 18.53 km, which is the figure to hold against the 10.8 km of the longest single subaqueous tunnel in the record.

Tokyo Aqua and Changxing are compared here on the figures this archive records for each, taken from the same sources and the same measurement convention. The 1990s account for 28 entries in this archive, and Tokyo Aqua is one of them, which is the context a single opening date does not carry on its own.

Across every class this archive records, Tokyo Aqua stands 162nd by length and Changxing 163rd, so the pair sits inside the top 163 of 244 structures. 38 other structures in this record opened within two years of Changxing, which is the cohort it was designed alongside and the fairer comparison for how it was built.

Reading the figures

Tokyo Aqua is the longer of the two at 9.58 km, ahead of Changxing at 8.95 km, a difference of 0.63 km. Subaqueous tunnels are governed by rock cover above the bore rather than by the depth of water above that, which is why depth and length are separate records.

Among the subaqueous tunnels this archive records, Tokyo Aqua stands 2nd by length and Changxing 3rd, adjacent in the ranking. Portal design follows avalanche and rockfall exposure rather than architectural intent. An immersed tube is built on land and sunk into a dredged trench, so its length is fixed before it reaches the water.

A hard shoulder inside a tunnel is expensive width, which is why a breakdown there is treated as an emergency. Water management is the maintenance problem that never ends, and drainage design decides its cost. Trade reporting is faster than official publication and less reliable, which is why opening dates sometimes move after the event.

161 recorded structures are longer than Tokyo Aqua, the nearest of them Duplex A86 at 10 km. Structures still under construction cannot hold a record here, and are listed separately until they carry traffic. This archive has held per-country and per-class tunnel inventories since the late 1990s, compiled from operator and administration sources.

Sources are named on each structure's own table. A national administration publishes what it maintains, so a crossing that changes owner can move between lists. Round figures in an old record are usually estimates that hardened into fact. Escape provision has changed more over the past forty years than excavation method has.