Changxing vs Bømlafjord: length, opening date and class compared

• 5entries listed

Side by side

Changxing is recorded on data/subsea.html and Bømlafjord 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

Changxing and Bømlafjord are compared here on the figures this archive records for each, taken from the same sources and the same measurement convention. Driven end to end the two would run 16.88 km, which is the figure to hold against the 10.8 km of the longest single subaqueous tunnel in the record.

Changxing is the longer of the two at 8.95 km, ahead of Bømlafjord at 7.93 km, a difference of 1.02 km. 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 Changxing or Bømlafjord has had.

Both belong to the 2000s, so the two were specified against the same expectations and the length difference is not standing in for a change of era. 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.

Across every class this archive records, Changxing stands 163rd by length and Bømlafjord 164th, so the pair sits inside the top 164 of 244 structures. The 2000s account for 53 entries in this archive, and Bømlafjord is one of them, which is the context a single opening date does not carry on its own.

That gap is about 11 per cent of the longer bore, which is the figure worth holding on to rather than the raw metres. Comparing two tunnels on length alone is the question most readers ask and the least informative answer available, which is why the differences that matter are set out below.

Reading the figures

A length quoted to the metre implies a survey that was actually carried out, and not every published figure carries one. Height above sea level is a separate record from length. Ventilation shafts allow a longer bore to be driven, and their absence is often what caps a tunnel's length rather than money or ambition.

Both are recorded in this archive as subaqueous tunnels, so the measurement convention is identical and the comparison is direct. Ventilation arrangement caps how long a bore can be driven more directly than money does. Base tunnels replaced summit lines that climbed by spiral and switchback, and several of those older routes survive above them.

Among the subaqueous tunnels this archive records, Changxing stands 3rd by length and Bømlafjord 4th, adjacent in the ranking. 162 recorded structures are longer than Changxing, the nearest of them Tokyo Aqua at 9.58 km. The rock between the portals decides the programme, and two bores of equal length through different geology are different projects.

Gradient limits are the main reason a railway crossing runs longer than a road crossing of the same range. A ruling gradient set by the heaviest train decides whether a rail crossing needs a tunnel at all. A comparison of two crossings is a comparison of two ground conditions, and the length column records neither.

The note column carries the qualifications. A record only moves when one project completes. Linings are inspected on a cycle of years and repaired in windows of hours. Blank cells mean the value is not on record. Compressed-air working made shafts through wet ground possible at a cost paid by the men who sank them.