Probably around 1988 when I was based in Seven Kings (East London/Essex borders) and playing in a brass band in Northfleet (Gravesend, Kent) and decided to cycle instead of getting the train. Straight down the A13 (Decades pre-dual carriageway**) from Dagenham to Purfleet on the way to the Tilbury ferry! At teatime!
I planned the route on the only map I then possessed of the area, a 1:250,000 scale Routemaster map.
Approximately every second vehicle was a container truck on the way to Tilbury Docks. I believe they
may have diverted from a straight line to overtake me, possibly by as much as 3 or 4 mm.
The following day, I went to the local WH Smith and purchased the 1:50,000 scale maps of the area and planned a somewhat longer, but much safer, route to Tilbury via the lanes around Upminster and Ockenden.
By contrast, the time I rode along the A1 from Markham Moor to Gonerby Services and back at night (in the early 90s) was virtually deserted by comparison!
** This section was built as 3 lanes, one for each direction and a middle lane for overtaking!
By the time I went down it, the middle lane had been closed and filled with traffic islands to prevent overtaking. Sadly, that included attempting to prevent the overtaking of bicycles as well as motor vehicles!