What was the original planned alignment for the A21 Sevenoaks bypass?

[Peter350]

Reading the interesting article on CBRD’s motorway database about the A21, I learned that the section of Sevenoaks Bypass to the south of Gracious Lane was originally intended to be on a different alignment north of the current road. This was because of landslips occurring on the then uncompleted stretch which meant the road would not be safe for use by motor traffic, so a new alignment had to be drawn up late into the construction of the bypass with the old one being torn up before it had the chance to see a vehicle driving on it.

What I would be interested to find out is where this original alignment actually went. CBRD states that it was 250m north of the current A21, but looking at modern overhead imagery there is very little evidence to suggest that a road could have been there. I’ve attached a map with two lines (shown in pink and blue) depicting possible routes I guess it could have taken, so it would be good if you could describe its actual route based on my projections.

Also, what type of Junction was planned for the eastern terminus of the original alignment?

[RichardA35]

BGS borehole viewer is your friend in these sorts of cases - click on the borehole scans and zoom in although beware of other linear alignment features such as sewers etc

[Telstarbox]

Not a geology fan but that is class

[Chris5156]

Richard's BGS map shows the line perfectly. The original alignment re-joined the present where the road turns south again, and from there it was again as built. The only realigned section was through that double bend, so no junction changes were necessary.

[jervi]

The BGS site is great. You can even see exactly where the M23 was going to blast through London!

[Nathan_A_RF]

I walked footpaths around the abandoned section a while ago to see if there was any trace of the old road but there is no hint at all apart from some odd treelines only visible from above.