Karmøy vs Oslofjord: length, opening date and class compared

• 5entries listed

Side by side

Karmøy is recorded on data/subsea.html and Oslofjord 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

Karmøy and Oslofjord are compared here on the figures this archive records for each, taken from the same sources and the same measurement convention. Karmøy belongs to the 2010s and Oslofjord to the 2000s, two decades in which what a tunnel had to provide by way of escape and ventilation was not the same thing.

Karmøy is the longer of the two at 7.74 km, ahead of Oslofjord at 7.39 km, a difference of 0.35 km. Driven end to end the two would run 15.13 km, which is the figure to hold against the 10.8 km of the longest single subaqueous tunnel in the record.

That gap is about 5 per cent of the longer bore, which is the figure worth holding on to rather than the raw metres. 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 Karmøy or Oslofjord has had.

Across every class this archive records, Karmøy stands 167th by length and Oslofjord 168th, so the pair sits inside the top 168 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.

The 2000s account for 53 entries in this archive, and Oslofjord is one of them, which is the context a single opening date does not carry on its own. Emergency lay-bys are spaced by regulation rather than by geometry, and their interval dates a crossing as clearly as its opening year.

Reading the figures

Salt water attacks reinforcement differently from fresh, and subsea linings are specified accordingly. Twin-tube crossings frequently carry two slightly different lengths, because the two carriageways rarely follow exactly the same line through 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.

Both are recorded in this archive as subaqueous tunnels, so the measurement convention is identical and the comparison is direct. 166 recorded structures are longer than Karmøy, the nearest of them Eiksund at 7.8 km. Cost figures are excluded throughout this archive, because currency, inflation and differing project scope make them close to meaningless in comparison.

Sequential excavation is slower per metre and far more tolerant of ground that changes without warning. Tunnels are regularly repurposed, and the mode a bore was built for is not always the mode it now carries. Toll revenue is usually pledged against the debt that built the crossing, and the toll ends when the debt does.

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, Karmøy stands 7th by length and Oslofjord 8th, adjacent in the ranking. Opening dates refer to the admission of traffic, not to breakthrough, which normally falls a year or two earlier.

The first long bores were driven by hand and gunpowder, and their alignments still show it. Both structures link to their own class table. A record only moves when one project completes. The oldest crossings still carrying traffic were built before any of the codes that now govern their upkeep.