At face value, modulating headlights on motorcycles is a great thing. A light that appears to be flashing is a great safety blanket against drivers who violate right of way of motorcyclists and claim they never saw the rider.
That conception is wrong.
To kick things off, modulators are annoying as all get-out. A light modulating at three to four Hertz, which all bike modulators do, appears flashing. This rapid cycling between low power and high power is especially annoying to folks driving small or low cars. Even huge SUVs aren’t immune to modulators paired with poorly aimed headlights. But we all adjust our headlight for extra load in the back such as a passenger, right?
What strikes me is the downright rudeness of some riders. Knowing your modulator is causing motorists discomfort but seeing this as acceptable because the rider believes they will be seen better with it is silly. This is the same incorrect line of thinking of “loud pipes save lives.” The image of motorcycling is tarnished, ostensibly for safety.
There is a dearth of studies about the subject. Right away something doesn’t pass the sniff test - the manufacturers of these devices would be shouting from the rooftops if there was a shred of evidence supporting their purported safety benefits. Even in today’s lawsuit-filled world, some careful wording could let the marketing department drive up sales like nobody’s business.
I did find some studies done a few decades ago. To start, there is a study that was done in the United Kingdom in 1985. This is available as SAE paper 856129.
The paper used three testing methods. The first was lab based with static photos, so we’ll not concern ourselves with it - modulating headlamps don’t translate to still photos.
The second test was a field trial involving interviewing pedestrians about motorcycle conspicuity. Once again we’ll pass over this since the mindset of a pedestrian is different than a driver. Also, pedestrians also rarely violate a rider’s right of way and cause harm.
The third testing method involved drivers as subjects. This is the most applicable test for our purposes and the results for the two “flashing” lights trials were: no benefit at any site and benefit only at one site for the other. Not a glowing endorsement.
SAE paper 900749, published in 1990, uses the previous paper as one of its sources. One of the points in this paper is: a single light provides poor location and speed cues. Modulators do not overcome this limitation!
The paper’s conclusion was a large dipped headlight, a pair of daytime running lamps or a fluorescent jacket all significantly helped daylight conspicuity.
The third and final paper is one that points to headlight modulators improving motorcycle conspicuity. This is the Olson report, published in 1979 for the NHTSA. Yes, the only paper supporting modulator use is also the oldest.
The Olson paper used one of the better testing methods. Using real traffic, the gap-acceptance rate was used. Basically, the rate at which motorists will violate the motorcycle’s right of way. Think the usual left-turners crossing your path or pulling out in front of you from the right.
Their results for daytime conspicuity, from gap-acceptance, was the following three items improve motorcycle visibility: a headlight modulating at 3 Hertz, any headlight being powered and wearing a high-visibility garment (fluorescent). Yes, they put running any headlamp at all on par with a modulating headlight.
The study goes in depth into peripheal versus foveal (central one to two degrees) vision. A postulation was made that the results of peripheral processing will selectively determine where the foveal attention will be directed. In other words, the brain of a motorist will determine what to look at.
Later, the paper says that no claim is being made that fixation of a target is also a sufficient condition for efficient identification. This means while drivers may look at a rider because of the modulating headlamp, they may still fail to see the rider. Every rider who has made eye contact with a driver and had the car violate their right of way anyways know exactly what this means.
Before we get into the fact drivers looking at riders does not necessarily mean anything, let us not forget the study states “the advantage of flashing light is absent in the presence of other flashing light.” More riders using modulators means a lower chance it will have an effect on motorists.
Another item in the study is the fact that for less than three second gaps, a motorcycle with a dimmed headlight and the automobile control are not statistically different. So if the gap in front of a rider is less than three seconds, the rider’s right of way is just as likely to be violated as a full sized car. To be more specific, a 1969 Plymouth station wagon, the control car. Motorcycle visibility is already on par with huge cars in this situation!
A page later, an important few sentences appear:
If we motorcyclists started slapping modulating equipment on all our bikes, we could be back to square one but with lighter wallets. Drivers will update their peripheral filters to ignore the flashing light.[The modulating headlamp] may represent a novelty effect. If so, it would be expected to diminish were the treatment commonly employed.
We have two out of three papers showing very little to no improvement in conspicuity with a headlamp modulator. The third paper shows occasional improvement with caveats of the novelty effect and the fact their advantage disappears when more than one flashing light is present.
This is not a great vote of confidence.
A plea to riders contemplating a modulator for their motorcycle: please don’t. The little gain of which there is a small chance of receiving isn’t worth angering motorists. Be a polite road user: use non-annoying methods of improving your safety.
