Tunnels and Viaducts on the A51 Motorway in France, by Kilometre Point

• 21entries listed
• 1 kmlongest bore
• 6.2 kmtotal length

The record table

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

How this table is compiled

The 31 entries are grouped on the page under 15 headings — exit sinard-avignonet (partial). open: spring 2007 (4), durance (3), exit 22 sisteron sud (3), exit 19 forcalquier (3) and exit 17 cen de cadarache. dep. 13 (3) — a classification the table carries as section breaks rather than as a column of its own.

Lengths for France are recorded in metres which is how the operators publish them and why the shortest entry here reads as 42 m and not a rounded figure. The longest entry is 23.7 times the shortest and 5.4 times the median, which is the quickest measure of how uneven the table is.

The eighth longest is Durance at 0.29 km, which is about where this record stops being about record holders and starts being about ordinary infrastructure. On 3 of the structures here the two carriageways are not the same length, which is why the archive records each direction separately rather than one figure per crossing.

The route table lists 21 structures with a recorded length, giving both carriageways where the two bores differ. The material on this page is held in 10 captions rather than in running text, 82 words of it, each written against the image or row it belongs to by the compiler who put the page together.

The shortest recorded entry is 0.04 km against 1 km at the top, a spread of 23.69x across the same table. The captions name 16 distinct places and structures — Area, Open and Sinard-Avignonet among them — and those names are the index into the length tables where each is recorded with its own figure.

Reading the figures

The twelfth longest, (viaduct) at 0.19 km, sits close enough to its neighbours that which of them ranks higher depends on how each was measured. The tunnel / viaduct column names 20 distinct entries on this page, Uriol and Petit Brion among them, each traceable to the operator or administration record it was taken from.

The three longest entries alone account for 2.4 km of the 6.2 km on this page, which is 39 per cent of the total from 3 of 21 rows. Comparing one national list against a neighbouring one is more informative than reading either alone, since terrain and funding practice differ sharply across borders.

This page records the structures catalogued for France in a tunnel almanac maintained at this address since the late 1990s. Monestier de Clermont at 0.86 km and Baume at 0.55 km follow it, and lengths are given per carriageway because the two bores of a dual route are rarely cut to the same length.

The next two longest are Monestier de Clermont at 0.86 km and Baume at 0.55 km. The table on this page runs to 31 rows and records Tunnel / Viaduct, Direction Marseille, Direction Grenoble and Notes for each of them, which is the shape the original compiler chose rather than one imposed here.

Also recorded here are Uriol at 0.5 km and Du Crozet at 0.4 km. A tunnel list for France reads differently from a neighbouring country's: 0 of these 21 structures pass three kilometres, and the same journey time is bought with one long bore in one country and a dozen short ones in another.