@JugglingWithEggs the radar is a Cannondale thing (might not be specific, but my wife's bike is from them) - basically a vertical gauge that shows how close anything behind you is; the more lights the closer. Accurate for distance but not much detail on size, how far out they are when they go past, speed, etc.

I used to live near Cambridge and envied the city cycling - I used to go down the A505 from Royston towards Duxford for work and I'm just pleased the roads were quiet back then (and I think drivers more considerate?).

We're lucky up here; my commute was along Newcastle quayside and the river for a dozen years, all basically on cycle tracks/pavement. I wouldn't cycle through town by choice but because Newcastle's so small you can be in countryside really easily and the roads are generally quiet.

@JugglingWithEggs ah, I can see that being a serious issue.
Not sure if they would help but my friend used to ride with bar-end folding mirrors to keep an eye on his kids behind him.
My wife's e-bike has rear facing radar (well, proximity sensor) which might help.

Obviously, I'm predominantly thinking of things approaching from behind and am probably missing something important that I take for granted.