Songshan Lake vs Shenzhen: length, opening date and class compared

• 5entries listed

Side by side

Songshan Lake is recorded on data/rail.html and Shenzhen on data/rail.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

That gap is about 8 per cent of the longer bore, which is the figure worth holding on to rather than the raw metres. This archive separates 4 classes of structure and both entries here are indexed under railway tunnel, which decides the table each is ranked in and the convention its length was measured by.

At over twenty kilometres Songshan Lake sits in the small group of bores long enough to need intermediate ventilation and a full escape regime. Driven end to end the two would run 74.47 km, which is the figure to hold against the 57.1 km of the longest single railway tunnel in the record.

Songshan Lake and Shenzhen are compared here on the figures this archive records for each, taken from the same sources and the same measurement convention. The 2010s account for 69 entries in this archive, and Songshan Lake is one of them, which is the context a single opening date does not carry on its own.

Across every class this archive records, Songshan Lake stands 6th by length and Shenzhen 7th, so the pair sits inside the top 7 of 244 structures. 13 other structures in this record opened within two years of Shenzhen, which is the cohort it was designed alongside and the fairer comparison for how it was built.

Both belong to the 2010s, so the two were specified against the same expectations and the length difference is not standing in for a change of era. 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.

Reading the figures

Songshan Lake is the longer of the two at 38.81 km, ahead of Shenzhen at 35.66 km, a difference of 3.16 km. Both pass ten kilometres, which 161 of the 244 structures recorded here manage, so this is a comparison inside a small group rather than across the field.

Neither holds the record: Gotthard Base at 57.1 km is the longest railway tunnel recorded here, 18.29 km ahead of Songshan Lake. The longer bore is not the harder job. 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.

Shenzhen was designed under the modern regime, with cross-passage spacing and emergency ventilation specified from the outset. Among the railway tunnels this archive records, Songshan Lake stands 6th by length and Shenzhen 7th, adjacent in the ranking. Toll revenue is usually pledged against the debt that built the crossing, and the toll ends when the debt does.

Overburden at the deepest point sets the lining, and on a long crossing it varies more than the length suggests. A structure renamed after opening keeps both names in circulation for years afterwards. The rock between the portals decides the programme, and two bores of equal length through different geology are different projects.

5 recorded structures are longer than Songshan Lake, the nearest of them Shanghai Airport Link at 40.19 km. Fixed links change settlement patterns, so the traffic a crossing carries later is not the traffic that justified it. Cross-border schemes require two states to fund the same hole at the same time, which is why they take decades.