One question which two or three of you must have had while reading this website is "Which tunnels out there were longer than Tidenham?"

While doing some research on another topic our information-mining team remembered this question and duly produced this lovely table ranking the 29 Great Western tunnels which were over 1000 yards long based on their length. Once we have pictures of all of them it will turn into a much bigger webpage. Until then...

(The stretch of railway which the tunnel is on is mentioned under "route" with the two notable stations/junctions which the tunnel is between in bold. First rank is the tunnel's position in 1930 and second rank is its current position)

Quick guide to imperial measurements:

Rank	Name	Length (yards)	Route	Status and Notes
1/1	Severn	7669	Swindon - Patchway - Severn Tunnel Junction - Newport	Active. Formerly longest railway tunnel in UK. Originally longest tunnel in the world.
2/2	Chipping Sodbury	4433	Swindon - Patchway - Newport	Active
3	Rhondda	3443	Pontypridd - Treherbert - Cymmer - Bridgend	Closed. Longest tunnel in South Wales. Sealed and buried at both portals due to internal subsidence.
4/3	Box	3212	Swindon - Bath - Bristol	Active. Said that sun shines through it on Brunel's birthday.
5	Merthyr	2497	Merthyr - Hirwaun	Closed. Longest accessible tunnel in South Wales.
6/4	Llangyfelfach	1952	Neath - Llanelli	Active. Freight only Swansea avoiding line.
7/5	Caerphilly	1933	Rhymney - Caerphilly - Cardiff	Active
8/6	Halton (Sutton)	1922	Chester - Helsby - Warrington	Active. Scene of a fatal accident in 1851.
9	Wenvoe	1867	Barry - Pontypridd	Closed
10/7	Sapperton Long	1864	Swindon - Gloucester	Active. Part of the mainline to South Wales until opening of Severn Tunnel.
11/8	Patchway New	1762	Newport - Severn Tunnel Junction - Patchway - Swindon	Active. Single-line tunnel on double track railway so used only by eastbound trains.
12/9	Clifton Down	1751	Bristol - Avonmouth - Severn Beach	Active. Nine yards short of a mile. "Down" as in "hill" not " heading away from London".
13	Cymmer	1595	Bridgend - Maesteg - Cymmer	Closed
14/10	Colwall New	1585	Hereford - Ledbury - Malvern - Worcester	Active. Replaced inadequate Colwall Old tunnel
15	Colwall Old	1567	Hereford - Ledbury - Malvern - Worcester	Closed. Undersized and replaced in 1929. Now occupied by a bat colony.
16	Pontypridd	1323	Barry - Pontypridd	Closed. South portal on grounds of University of Glamorgan Pontypridd.
17/11	Ledbury	1318	Hereford - Ledbury - Malvern - Worcester	Active
18/12	Patchway Old	1246	Swindon - Patchway - Severn Tunnel Junction - Newport	Active. Single-line tunnel on double track railway so used only by westbound trains.
19	Ballingham	1206	Hereford - Ross - Gloucester	Closed
20	Tidenham	1190	Chepstow - Monmouth	Out of use. Track in place but tunnel fenced off.
21	Pinnock	1173	Lostwitheil - Fowey - Par	Out of rail use. Now a lorry road for china clay traffic to Fowey Docks.
22/13	Ardley	1147	Banbury - Aynho - Bicester - High Wycombe	Active
23	Gyfylcha (Tonmawr)	1109	Port Talbot - Tonmawr - Cymmer	Closed. Scene of a fatal accident in 1902. North portal collapsed in 1947, closing tunnel.
24	Whiteball	1088	Taunton - Tiverton - Exeter	Active. Descending to Taunton from this tunnel City of Truro achieved 102.3mph in 1904.
25	Bullo (Haie Hill)	1065	Newnham - Cinderford	Closed. Longest tunnel in Forest of Dean.
26/14	Somerton	1053	Castle Cary - Taunton	Active
27/15	Dinmore	1051	Hereford - Leominster	Active
28/16	Bristol No.3	1017	Bristol - Bath - Swindon	Active
29	Cwmcerwyn	1010	Port Talbot - Maesteg - Pontyrhyll	Closed

The oldest tunnel featured on this list is Bullo, also known as Haie Hill. When opened in 1810 it was the longest railway tunnel in the world - although it was only used by a horse-drawn tramway for the first couple of decades, which meant that the steeply-graded bore didn't have to feature annoying things like ventilation shafts which might have allowed steam locos to work trains through it with any degree of comfort. The tunnel closed in 1965 after a working life of 155 years - something which several of the active tunnels featured here haven't achieved yet and most of the closed ones never got anywhere near. Both portals are still visible - this is the west one - but have been firmly sealed up with brick walls. There is a certain degree of optimism with the three tunnels on the former Newnham-Cinderford line that they will never need maintenance again.

Now the longest visible tunnel wholly within South Wales, Merthyr - also known as Abernant - Tunnel is unusual for having completely mismatching portals. This is the single-line east portal, from which trains descended over various long-gone junctions to Merthyr Tydfil. The west portal was wide enough for double track, although the tunnel only ever took a single running line. Abernant is slightly curved at each end, providing a dead straight central mile between the portals which has never seen sunlight, the tunnel having no ventilation shafts. During its career it was mostly noted for an occasional habit of falling in at short notice. It closed in 1964; re-opening to rail transport is unlikely for some reason but, equally curiously, the cycling lobby are starting to show an interest in it. Until then, the wall just inside the portal is graced with a sign explaining that it is a private tunnel with no public right of way.