Some synchronicity here as I had just been reading about this in
@RuthRoperWylde 's excellent "Roadmap of British Ghosts vol 2"
Gracious Lane was used as a temporary diversion in 1967 when the by pass was built:
"An extension southwards to a temporary junction with Gracious Lane opened on 16 January 1967. It was for northbound traffic only. A section south of here had to be rebuilt on a different alignment owing to landslips because of the slippery clay sub-soil. "The Builder" reported that advice at the planning stage from local farmers was ignored and the piers of the Hubbards Hill Bridge were at 5 to 10 degrees from vertical within a few weeks. The diversion was to cost an extra £1.2 million. To compound matters the new Morants Court bridge was having to be partially rebuilt owing to porous pockets in the concrete caused by a breakdown in the pouring of concrete one night."
Source:
https://www.sabre-roads.org.uk/wiki/index.php?title=Network_changes_-_1960s
Also the more detailed article@Floyd1 posted on the unwhinge thread. Link here:
https://www.roads.org.uk/motorway/a21
Currently Gracious Lane is at a much higher elevation than the A21
View attachment 74111
and had become a "popular" site for suicides leading to petitions to make the bridge safer.
This from
https://www.change.org/p/sevenoaks-...d-rails-on-gracious-lane-bridge-to-save-lives
"A number of people have sadly taken their lives by jumping from Gracious Lane bridge over the A21 in Sevenoaks. There are Samaritans signs on the bridge but we need to do more to protect both the people who are considering jumping and those that are at risk when driving on the A21, not only from seeing someone jumping from the bridge but also the risk of serious injury.
By introducing high guard rails people will not be able to jump."
I'm not sure about that, it is more difficult for them to jump, certainly but not impossible. The road works for this took ages with local MP getting involved in the length of time taken, road closures, etc.
I'm not sure (still looking) whether what is now "Tonbridge Rd" on the south of Sevenoaks used to be designated the A21 before the by pass was built. That certainly had and still has a level junction with Gracious Lane.
Here's streetview looking north: