The top light is a helmet-mounted light. They mention this in the full paper but it’s not clear from the abstract.
Creatures with forward facing stereoscopic vision (like us) can judge the speed and distance of an object if we can determine its size and see something of the background. In the dark, some information is missing when we rely on attached lights.
Most people know the approximate size of a car, and so with two lights its easier to guess the distance (and crucially speed as the distance between the lights seems to change).
I've noticed it's harder to cross a road when bikes are approaching than cars, because if you're looking along the axis of travel then its hard to gauge their speed.
Attaching more than one light to a bike allows us to judge the speed better. It seems that it's irrelevant whether the spacing is horizontal or vertical for our visual systems to make this judgement.
Customized cars often project vanity mood lighting down towards the pavement. (I believe the legality of such nonstandard lighting varies across jurisdictions.)
Perhaps motorcycles could be required to project a large light-splash down, creating a more-visible 'light puddle' below them. It could even be something with very-sharp boundaries, & a standard oval size, so that the shape more strongly communicates distance/angle/speed.
I've seem bicycles in London projecting a green bike emblem into the road about 5 meters ahead using a laser.
Two somewhat higher intensity spots on the road ahead would work as you indicate, At least in ideal road conditions.
Re. b)If a bike comes up really close to the rear of your vehicle, and the rider has no reflective gear, the light can be obscured by your own vehicle.
Re. a) I’m not sure if this is some Aussie thing. Especially with push bikes. The number of people I’ve seen on the road at night with no lighting and zero reflective gear.
From what I understand the reflector stuff is routinely ignored by 'the community' because it's outdated, rules out use of clipless setups etc.
But the lights ... no idea. It's really really bad idea to cycle on the road at night with no lights. I wouldn't want to risk it, and it's scary as a driver when all of a sudden there's this dark figure out of nowhere.
Can really help with retro-reflective signage, since I can point a light directly at the sign. But definitely not a blinding return.
Similar to https://www.aliexpress.com/w/wholesale-bicycle-laser-tail-li...
One issue is: - Propensity of people to use "lasers" for this, see above link. - Bikes with and without motors, lean to the side. - People don't like lasers being flashed in their eyes.
But even motorbike foglights, turned almost vertically down at the road, would achieve something like this.
Works great for getting a driver’s attention at a 4-way stop (the North American approach to right-of-way is deficient when everyone stops at the same time and is going straight).
But a problematic tell when I see a head-turner walking on the sidewalk.