What about headlight modulators

(Originally published on FB 25 March 2019, mildly edited)

What about headlight modulators?

Headlight modulators have been the subject of investigations on a number of occasions, and some US-based riders swear by them. So I was interested to be sent the link to this particular promotional video.

The video starts with a demo of the rear modulator…

…unfortunately, I didn’t even SEE it first time the video ran, which should tell you something.

I know the bike’s not going very fast, but arguably, by the time it comes on it’s too late – the bike’s already slowing. Given that the usual cause of a rear-ender is being tailgated by a vehicle that’s too close to slow down when the bike ahead decelerates, what’s needed is a ‘pre-braking’ warning, not something that comes on at the exact same moment. How you achieve that, I’m not sure.

And there’s a more serious issue. The flashing light around the index plate is actually pulling your eyes AWAY from the important signal, which is the brake light. I can conceive of a situation where the driver’s eyes are pulled down to the flashing lights and fails to react to the brake light. After all, flashing lights around the index plate are usually there for decorative purposes rather than any function.

So what about the front modulator?

You can certainly see it but it’s a bit irritating, to say the least. Can you imagine driving against a long line of bikes, all flickering away on high beam?

In any case, the result of US research seems to be that it enhances DETECTION at long distances – we’re talking hundreds of metres away. So maybe a less irritating modulator may have some benefit on the kind of fast, flat and straight roads they have in parts of the US or perhaps Australia. I can see one use being to alert drivers who might consider overtaking towards the motorcycle.

However, as an anti-SMIDSY device in urban areas, my impression is that modulators appear ineffective, and as far as I can tell from research, the modulator doesn’t appear to have any significant conspicuity benefit when the range is twenty metres or less.

Why is this distance important?

Because in an urban context it’s the crucial distance at which you MUST be seen. Collision dynamics in slower-moving, denser in-town traffic – the circumstances in which most SMIDSY-style crashes occur – clearly indicate that at the moment the the driver makes the final and crucial ‘looked but failed to see’ (LBFTS) error, the bike must be with twenty metres, and probably within a dozen metres or so.

It doesn’t actually matter if we’re spotted 500 metres away or fifty metres away – the ‘Last Chance Saloon’ for the rider is the last check the driver makes before turning into the bike’s path. Why? Two reasons. If the bike is further off when the error happens, either the emerging car will clear the bike’s path and it will be a near-miss, or the rider has sufficient space to hit the brakes hard and stop which means it’s another near-miss.

So the implication is that the bike actually has to be much closer than most riders realise before the LBFTS error will inevitably result in a collision.

What’s clear from looking at the crash stats is that neither hi-vis nor DRLs seem to have made any difference to the overall pattern of crashes, and so the ‘Sorry Mate’ collisions at junctions remain as frequent as ever, despite significant numbers of riders in hi-vis riding kit and virtually every bike in the UK now using lights in daytime.

I doubt we’d see any difference if modulators were legalised for use in the UK either.

Of course, the counter-argument is that modulators will help drivers see you further off, then they will remember you’re there, but I’m not convinced. There’s no evidence that it works for ordinary lights despite trials suggesting bikes with lights are seen at greater distances than bikes with no lights.

So, from a personal perspective, just as I don’t rely on DRLs or hi-vis clothing, I’d rather back my ability to see the driver and anticipate the error than put my faith in a modulator.

In any case, they are illegal in many countries.

Thanks to ‘Paul’ for alerting me to the link.

2 thoughts on “What about headlight modulators

  1. Hi Kevin,

    Interesting post. I’ve recently looked at purchasing a https://st2-systems.com/st2-brake-module/ .

    Looking at the promo vids etc it looks like a value for money additional safety system that highlights to any following (more often than not, too close larger vehicles) that you are using acceleration sense to modulate your tracking speed to manage safe distance between you and hazards ahead of you.
    There are two reasons I have considered the modulator.
    1. My son riding his 125cc to work was nearly rear ended, turning (indicating in plenty of time) into a left hand junction- In inclement weather. Driver behind not paying enough attention or just assuming my sons path of travel was straight ahead??
    2. Twice I’ve had to travel in bad stormy weather at night on B and A roads, with extremely poor visibility, and vehicles up my rear with no idea when I was using acceleration sense to manage my riding plan. I know we can dab the breaks to highlight adjustments in speed, but with so many hazards and weather related issues to process, a modulator’s additional visual benefits can’t be ignored??


    • Something I repeat as often as I can is that as soon as we slow down, we shift the biggest threats from ahead (that’s why we’re slowing) to behind…

      …and we can do little about how the vehicle behind behaves.

      I learned the hard way myself that watching the mirrors is vital – the old ‘mirror signal manoeuvre’ line that’s taught to new riders and drivers is not nearly enough… it should be more like mirror – signal – mirror – mirror mirror [to check the vehicle behind is responding] – manoeuvre – mirror [to double check].

      Indicators sometimes need help too – the much ridiculed arm signals are something I’ve talked about on a number of occasions but the movement of an arm often attracts attention that brake and indicator lights don’t – particularly in bad weather.

      I have just a single brake light on my own machine and I’d much prefer twin bulbs and a bigger tail light.

      Flashing lights are dubiously legal I would have said, and it still requires the following driver to see, then respond.

      £100 is quite a lot… maybe simply fit an auxiliary light or two to the brake light circuit?


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