I was in Arnos Park yesterday, a large and pleasant park in Enfield just to the north of Arnos Grove station. It has two prominent physical features, one of which is the Pymmes Brook which was flowing fairly strongly after all that rain we've had. The other is the Arnos Park Viaduct, a long brick structure which was built in 1932 to carry the Piccadilly line across the valley of the aforementioned river.
The viaduct is over a quarter of a mile long and supported by 34 arches, and if you get it at the right angle can be very photogenic. It's a particularly appealing structure because you can actually walk underneath it, stepping through the arches via separate arch-shaped openings and looking ahead through a curve of corresponding gaps. Other splendid brick arches like this exist elsewhere in London, for example the Dollis Brook Viaduct on the Mill Hill East spur of the Northern line and the WharncliffeViaduct over the river Brent in Ealing. But I think the Arnos Park Viaduct is the longest you can actually walk properly underneath as opposed to just under, certainly anywhere on the tube network.
And that got me wondering...
What's the longest distance you can walk underneath something in London?
Most of the Underground runs either underground or on the surface, with bridges and viaducts very much the exception. Being able to walk underneath those viaducts is rare, at least other than via a normal pavement or subway, which is why I think Arnos Park offers the longest walk of the lot. It's not the full 34-arches-worth because the ends of the viaduct are either too low or too filled-in, plus the Pymmes Brook itself creates an obstacle that can't be crossed on foot.
By my calculations the section of viaduct to the north of the river creates a covered space about 70m in length whereas the southern section is a much longer 160m, this before a few of the arches start to be filled in for use as backrooms, lockups or somewhere for the Friends of Arnos Park to store their litter-picking facilities. But 160m is a pretty good length to be walking underneath a working railway, intermittently hearing the tiny tube trains rattling across the top.
The DLR spends a lot more of its time in the air, indeed it's the most viaducty of all London's railways, hence the excellent views you get while whizzing across Limehouse, Deptford or Docklands. But the longest section you can actually walk underneath is on the Woolwich branch as it runs through Silvertown, immediately alongside North Woolwich Road, and covers a substantial stretch of the pavement. Start by the Silvertown Viaduct and you can stay immediately underneath the viaduct by following the pillars all the way to the Connaught Road junction, passing directly beneath West Silvertown and Pontoon Dock stations along the way. Admittedly there is one spot near Barrier Point Road where a safety barrier nudges you out fractionally and another near West Silvertown where a future building site marginally intervenes, but amazingly this under-railway jaunt is well over a kilometre long.
The longest walk under a railway: erm
If we broaden our scope to non-TfL rail lines in London, these more often run at height so there should be a good chance of finding a walking route directly underneath. But again a lot of under-viaducts are inaccessible to the public, their arches hired out for use by very small businesses, or only duck-under-able along a very short stretch. So where in the capital might be the longest covered walk beneath a stretch of railway tracks? I'm not exactly sure. I considered the shop-lined hike between London Bridge tube station and London Bridge railway station, but I don't think that goes much above 150m. I considered The Sidings, the half-dead shopping Centre underneath Waterloo's former Eurostar platforms which might be 170m all told. I considered the 200m passageway connecting both sides of Clapham Junction station which probably qualifies but isn't really what I meant. But I couldn't think of an actual bridge or viaduct that beats these, and wondered if you might be able to help me out because I bet I've overlooked something obvious.
London's not overblessed with actual motorways, we only have the M1, M4, M11 plus the M25 around some of the edge. But in terms of being able to walk underneath them I think we have a clear winner which is the M4 viaduct north of Brentford. When engineers came to plot the course of the motorway across the river Brent they chose to drive it through the grounds of Boston Manor House, creating a 17-span concrete centipede that despoils the far end of the park. The mix of nature and slab blocks is very much unlike anywhere else in London, and hardly any of the drivers speeding across the top realise it's here. Arguably the elevated section just to the east is a mile longer, but most of the pavement there isn't actually underneath the motorway proper.
The longest walk under a road: erm
My best guess here is the Westway through North Kensington, another 1960s viaduct but this time carving through a more residential area. The older Harrow Road passes directly underneath, like an exhaust fume sandwich, with actual pavements that local air-breathers can choose to risk. I'm not sure quite how long the walkable section underneath the A40 is, maybe 1000m, maybe more like 400m, and next time I exit Royal Oak station I should probably go and check. But there might well be a longer stretch of road you can properly walk under, somewhere in the region of a few hundred metres, and again I seek your suggestions for what I might have missed.
This is easier to ascertain. The widest river in the capital is the Thames and the longest foot tunnel underneath it is at Woolwich, has been since 1912. The tunnel itself is 504m long but some of that is needed to extend as far as the access stairs to either side, so the length that's actually underneath the river at high tide is more like 450m. It always feels longer.
Some subterranean Crossrail platforms are really long, as indeed are Crossrail subways, but we can beat those. The Rotherhithe Tunnel dips below the ground for a considerable length, which if you measure it comes to nigh exactly one kilometre from the northern portal in Limehouse to the southern portal in Rotherhithe. And it's officially walkable too, indeed I risked it for the centenary in 2008, not that I recommend any of you should follow in my footsteps. I can't think of anywhere else in the capital where you could spend a full twelve minutes at walking pace beneath the surface of the earth, not that's publicly accessible anyway, the mysterious secret Holborn tunnels being both off-piste and unquantifiable. If you know better, feel free to tell where me I'm going wrong.
