The top light is a helmet-mounted light. They mention this in the full paper but it’s not clear from the abstract.

My take is that this is about parallax [1], although I haven't read the paper and so that's an assumption.

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.

[1] https://en.wikipedia.org/wiki/Parallax

This research, & further your comment, makes me wonder:

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.

That's really quite a good idea.

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.

I’ve never seen this in Australia. But my main gripe with motor/push bikes is a) People riding without any lights. b) People riding without sufficient lightly.

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.

So as a relatively recent migrant to Aus, I find that odd because AFAICT the regulations here are more strict than back in the UK. I.E. you must wear a helmet, you must have lights after dark, your bike must have a certain configuration of reflectors (two in the wheel, back/front of each pedals, front and rear) etc.

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.

I suspect this would harm the motorcyclist's night-vision in a way that a car driver is not affected due to the light reflecting off the ground and right back at them. Whereas the body of the car protects the driver from the glare.

Rider here. It'd be out of my field of view when riding. A friend had such a system on his Harley and the visibility was helpful.

Bicycle rider with a somewhat weak top-of-helmet mounted light (maybe 100 or 200 lumens): I have a tough time telling if it's on while riding if it's somewhat bright. Zero impact to view.

Can really help with retro-reflective signage, since I can point a light directly at the sign. But definitely not a blinding return.

I use a 300 lumen one, and it's the same, reflection is just not a problem at any reasonable distance (like over a metre)

A good idea that needs more compliance/regulation work ahead of standardising.

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.

I just moved to the Netherlands where bikes are aplenty and saw one of these two nights ago. It was not so dramatic as the examples you linked but still very visible. I think this could be a good option for motorcycles.

Motorcycles also suffer a depth perception problem in the daytime:

https://www.youtube.com/watch?v=doSDfIo61r0

Yes, you're onto something. Ryan F9 has an amusing video that dives into the "pigeon issue" of mis-judging approach speed of oncoming traffic that results in one of the most common motorcycle accidents. https://www.youtube.com/watch?v=doSDfIo61r0

That has long been my practical intuition. To put add an additional issue, at a glance, a motorcycle light at night just looks like a car that's far away. That's definitely not going to work out well.

I have one of these on my bicycle helmet.

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.

Seriously! As a motorcyclist (and cyclist) with a keen interest in not dying, I'm always looking for additional ways to be seen and predictable. This image should have been in the blog article, full stop. How is it _so_ buried?

light is great but first on the list is an aftermarket horn .. LOUD

I was about to cruise through a yellow light today when a pickup truck in the center of a one way street abruptly decided to make a left turn across my path. (I was in the far left lane.) I slammed on my brakes and laid on my horn.

I saw his face in his mirror. As he realized the noise he was hearing was my underpowered Vespa horn protesting the needless near-calamity, a smirk of victory beamed across his face.

Guy nearly took me out today, and all I could do was trust my ABS brakes and give him Roadrunner's angriest "meep meep."

Now you've learned your lesson to not cruise through yellow lights. Also, mind your lane position. I'm always in the left-most position to maximize driver's opportunity to see me.

I can count on the fingers of one hand the times I used the horn on any of my motorcycles in two decades of riding (>100kmi, various situations, not much commute, less in the dark). In dangerous situation where honking might have helped, I typically was busy to either break or steer out of harms way. Aside that horns on m/c tend to be meek. They seem to be installed only because some law requires them.

In my part of rural Aus, the (weedy OEM) horn's indispensible for scaring wallabies out of the way at dusk.

you should publish videos on this to demonstrate for us in wallaby-less/wallaby-extinct locales.

I would if I could! Sometimes it's kind of funny - you see a few sets of ears poking out amongst the long grass of the road verge. A couple of beeps on the horn and suddenly a mob of wallabies emerges - and often hop straight across the road rather than back into the bush. That's the main use of the horn - to flush out the daft critters who may well otherwise jump straight into your path.

iirc most motorcycle safety coaches will advise that the horn is usually the last thing you should be thinking about in a dangerous situation. It's a great tool for getting someone's attention, but in an emergency the motorcyclist should focus all of their energy on maneuvering to safety regardless of how the car behaves. Motorcycles are maneuverable enough that generally if you have time to honk you have time to be proactive about your own safety rather than rely on the driver hearing you.

If you're able to focus on both that's great but most riders fall back onto instinct and that instinct should be braking, accelerating, or turning rather than honking.

The coaches tell you that because they're (mostly) talking to new riders and as you say working the horn isn't going to make a material difference and is bottom priority and ultimately clutters the mind of a new rider trying to deal with the situation.

After say 5+ years of riding bikes the braking/accelerating/turning as you say is instinct and the conscious part of the mind has plenty of bandwidth left to honk the horn :)

Totally. 5 years of smart, conscious riding will definitely give you that bandwidth, but I've also met people who've been riding twenty years tell me they "had to lay 'er down" in an accident as if it was the result of a planned maneuver and not a fistful of front brake as they shat their pants. Imo it doesn't matter how long you've been riding if you don't make the effort to hone the right instincts for when shit hits the fan.

By the time you use your horn it's too late for the most common fatal multi-vehicle accidents, which are crossing traffic incidents. Most motorcycle saftey courses tell you not to bother with the horn until you have the incident under control because people don't react predictably or in time to horns.

amazing number of downvotes on 'horn' -- actually, as an urban rider, the horn is very useful. Plenty of comments here have to do with the freeway or during an event that has already started.. thats not the purpose of a horn. The horn is to tell others you are there before an accident starts, in a setting where they can hear you. Amazing antipathy for a safety statement here..

What? You honk your horn every time you enter an intersection where a driver is present and could cross your path? Because if they're already crossing your path then honking your horn is the last thing you should be concerned with.

who said "every time" ?! what nonsense

This is a terrible conversation

Then maybe you should explain what you're actually doing because I'm an urban rider, my friends are urban riders, and the general consensus in our local motorcycling community is the horn is useless. Because like I said, if the driver isn't crossing your path then there's no reason to sound the alarm and if they're already entering/crossing your path then you'd better be engaged in crash avoidance. It's not clear when you're using your horn.

Loud horns don't overcome even louder sound systems and then there's the issue with deaf people (yeah, that's something that's happened to me before - why didn't they hear my horn? Oh, they were literally deaf!)

Most motorcycle crashes involving other vehicles are a result of drivers crossing the rider's path, e.g. making a left-hand turn in front of a rider who's going straight. Honking your horn in such a scenario can actually be a bad thing because most driver's response to hearing a horn is to stop. Now the driver is completely blocking the path and not moving. It's typically better to let the driver proceed and swerve to the left to avoid collision.

That's why most riders consider horns to be useless.

getting helmet mounted light charging would be a chore. what if we only keep the other 5 lights? would it be that much less effective?

Would it?

I already keep my Cardo helmet speakers charged. Cyclists keep their helmet lights charged.