Lights

So you're saying as the batteries' capacity slowly drops, traffic incrementally approaches your rear?

Yes.

They drive closer at a faster speed, as they see the light later. Best place for this example, is on the crest of the top of Loampit Vale. The cycle lane runs out at the top, and cars/trucks/murderers approaching fast from the bottom of the hill, DO give room because they see the red glow on the crest of the incline. When my batteries have been left too long, the glow is very dim, and cars pass at sometimes only 1-2 feet away, though when they have realized they've narrowly missed side-swiping me, they do a belated swerve....as if their cognitive processes have latterly just kicked in.