Eiksund vs Karmøy: length, opening date and class compared

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Side by side

Eiksund is recorded on data/subsea.html and Karmøy 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

Eiksund is the longer of the two at 7.8 km, ahead of Karmøy at 7.74 km, a difference of 0.06 km. Eiksund belongs to the 2000s and Karmøy to the 2010s, two decades in which what a tunnel had to provide by way of escape and ventilation was not the same thing.

That gap is about 1 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 15.54 km, which is the figure to hold against the 10.8 km of the longest single subaqueous tunnel in the record.

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 Eiksund or Karmøy has had. A crossing driven from both ends meets in the middle, and the survey needed to make that happen is invisible in the finished figure.

Across every class this archive records, Eiksund stands 166th by length and Karmøy 167th, so the pair sits inside the top 167 of 244 structures. 49 other structures in this record opened within two years of Karmøy, which is the cohort it was designed alongside and the fairer comparison for how it was built.

Neither holds the record: Sandoy at 10.8 km is the longest subaqueous tunnel recorded here, 3 km ahead of Eiksund. The 2000s account for 53 entries in this archive, and Eiksund is one of them, which is the context a single opening date does not carry on its own.

Reading the figures

Cost figures are excluded throughout this archive, because currency, inflation and differing project scope make them close to meaningless in comparison. An intermediate shaft turns one heading into two and leaves a structure on the surface for the life of the tunnel. A structure renamed after opening keeps both names in circulation for years afterwards.

Both are recorded in this archive as subaqueous tunnels, so the measurement convention is identical and the comparison is direct. A record for length has changed hands roughly once a decade since the 1870s. Transverse ventilation gives each section its own supply and extract, which is why the long two-lane crossings carry a false ceiling.

Karmøy was designed under the modern regime, with cross-passage spacing and emergency ventilation specified from the outset. Among the subaqueous tunnels this archive records, Eiksund stands 6th by length and Karmøy 7th, adjacent in the ranking. Pumps run for the life of a subaqueous crossing and are the one system that is never switched off.

165 recorded structures are longer than Eiksund, the nearest of them Qing-Huang at 7.8 km. Reconstruction after a fire is recorded because it usually changes both the profile and the ventilation arrangement. A base tunnel trades much greater length for a far lower summit altitude, which changes what the number means.

Only structures open to traffic are compared. Cross-passage spacing, fixed firefighting and emergency ventilation control are what modern tunnel safety regulation actually governs. Rock cover above the bore governs a subsea design, not the depth of water above that. The tail of a record is more representative of what gets built than its head is.