Thread by @time_nw

Many of you will be familiar with this image. I believe it was taken by Alan A. Jackson in 1965. It shows the submerged tunnel mouths of the uncompleted Northern Line extension, at the southern side of Elstree Hill. I've long wanted to know exactly where it was. Read on...⬇️

..the crazy thing is, it was actually quite easy. It didn't involve archive maps and geo-phys, or even Tony Robinson. I just did a Google search using 'Elstree South Tunnel'. Someone has actually pinned the site! .....

...however you won't find anything left. Despite the tunnels being bored and tunnel entrances built in the mid 1930s, work stopped in 1940 for obvious reasons. When the project was abandoned in the late 1940s, the tunnels were partially filled in and left derelict. TBC...

If you recall, Alan's photo was taken in 1965. This 1964 photo gives you a good idea why the tunnel entrances were wiped away from the landscape. The works that took place for the extension of the M1 through to Mill Hill....

...and the necessary interchange roads, together with a new roundabout.

Image via @Mikeashworth12

@Mikeashworth12 Despite the works not being on top of the tunnel mouths, the activity around the site presumably necessitated (or gave a good reason) the opportunity to get rid of them.

@Mikeashworth12 But the thread doesn't stop there (sorry!). What I wanted to see was any trace of the tunnel entrances on period maps. So I went onto the wonderful @natlibscotmaps and rooted about. I didn't find maps, but I found something far more interesting...

@Mikeashworth12 @natlibscotmaps In 1944/45 the Government got the RAF to do an aerial photographic survey of the UK. This would allow them to see the true extent of wartime bomb damage & enable postwar planning. The RAF had experience of this kind of work from wartime reconnaissance of enemy locations...

@Mikeashworth12 @natlibscotmaps @natlibscotmaps have much of this aerial survey, and it's accessible to all. Here is the image I located. Its not the sharpest image, but we are looking down onto the area where the tunnel mouths were. Look in the top left of the image...

@Mikeashworth12 @natlibscotmaps Here's a pointer for you. I have then zoomed in and added some density. It's not too clear as a structure, but that's the start of the tunnel, because leading up to it is the path of what would have been the Northern Line, is it came from Edgware.

Once I'd found this, I was curious to trace the route of the proposed extension. Remember, these images were taken only a few years after work had stopped on the project, so it is quite easy to see the cleared path. So here we are tracing back from the tunnel, back to Edgware.

We are now looking down on the A41 going left to right, and the Spur Road roundabout. The feint dark lines are the remains of the brick arches many of us are familiar with. This was where Brockley Hill station was going to be, and the open land would have been developed.

We have now crossed the A41 and the line is visible as a gap between the housing that had gone up in the 1930s. We are going from top to bottom, diagonally.

We are now about to hit the centre of Edgware. If you are having trouble seeing the route, don't worry, I'm going to do a highlighted version straight after this bit!

Now we have reached our destination. Station Road, Edgware. The line would have gone under the road and joined the existing station, which had opened in 1924, as an extension from Golders Green.

Here's the highlighted version.

I'm sure you are exhausted now, but here's some bonus bits!
Using the @natlibscotmaps overlay function, here's the Elstree South Tunnel entrances on their own in 1944, and then with a ghosting of the land today.

Here's a thread I did a few years back, where I marked up a 1980s AtoZ mapbook and walked the route from the A41 back to Edgware.

https://twitter.com/time_nw/status/1251157282156457985?t=o01lBea8Yj1d2lTlDCWXug&s=19

Another thread from more recently

https://twitter.com/time_nw/status/1775086212065227012?t=yWkPVOR1W-5-72y8vCz2hg&s=19

That's it. I promise. Thanks for sticking with me on this daft excursion through time. I'm now going to sit in a darkened room for an hour! My thanks to @natlibscotmaps for providing such an invaluable website.