Visibility on a Scooter - Z-Motion, X-Motion, and Why Cars Pull Out in Front of Us

Anybody who has ridden a scooter or motorcycle for any appreciable amount of time knows the all-too-familiar feeling that we seem to be invisible on the road.

When the umpteenth person pulls across our path or pushes us out of our lane, it's tempting (and quite natural) to get very annoyed at the distracted and inattentive driver.

In this article, I hope to provide an insight into the psychology of visibility, and offer some tips which can help.

Z-Motion

I know that may sound uncomfortably like a substance advertised on the back pages of seedy magazines, but it is actually a large part of the reason why so many drivers pull out in front of scooters and motorcycles.

You see, the human eye is most sensitive to movement that crosses its field of vision (right to left, or left to right). This is know as X-motion, and the eye is very good at detecting it.

On the other hand, movement directly towards the eye (z-motion) is much harder to detect. In fact, the eye usually only detects such motion when the object in their field of vision presents some x-motion by taking up much more space in their view - and so presenting x-motion by virtue of the fact that it "grows" quickly in relation to the background.

Are you beginning to see the issue that us scooter riders have to deal with?

Compared to a larger vehicle, we present little-to-no x-motion when approaching a vehicle. A larger vehicle, such as a car or truck "grows" in a person's vision at a much faster - and linear - rate. It presents much more horizontal movement in relation to the background - even when coming straight towards the viewer.

Try this experiment when you are next at the side of a road: Watch a car coming towards you. You will see how it's "growth" in your vision is quite linear as it comes towards you. It steadily grows and grows until it reaches the point where you are standing.

Now, watch a scooter or motorcycle. You will find that its apparent size in your vision remains small, small, small, right up until it is very near to you, when it suddenly "grows" at an exponential rate.

"I'm so sorry! I just didnt' see you!"

This is precisely why many drivers will pull out in front of us, then suddenly slam on their brakes at the last second when they finally see us.

Unlike a larger vehicle, as we approach a driver, say, at a junction, we present very little for the driver to see right up until the last moment when we "grow" exponentially in their vision.

So much for the theory. What can we do about it?

Well, it stands to reason that, having identified the root of the problem - z-motion (or lack of x-motion), the way to deal with it is to do anything that presents more x-motion to the driver.

You could consider this very simple and common-sense tactic related to your position in the road.

Imagine you are riding along a straight road, and approaching a junction on your right where a car is waiting to leave the junction.

The nearer you are to presenting a straight-on movement to the driver, the less x-motion you are presenting. The harder you will be to spot. By riding in the right of your lane, you are ensuring that you are riding straight towards the driver's vision. You are presenting mostly undesirable z-motion.

Just by virtue of moving to the left of your lane, your are presenting much more x-motion to the driver. There is a greater angle between the driver, and the rider. As you continue towards the driver's position, much more x-motion will be introduced to the driver's vision.

Further, by the very act of shifting to the left of the lane, you have presented x-motion to the driver while doing so:

The other advantage to this is that you have also created a "buffer zone" between you and the car, should the driver pull out.

Once you have passed the hazard, you can smoothly resume your commanding position in the middle of your lane.

Passive Tactics

I see much written about various tactics to increase your visibility to drivers - ranging from riding with high-beam on (seriously??), headlight modulators, to high-visibility clothing.

Of all these, my opinion is that the most useful is to wear bright "dayglo" clothing

I would also highly recommend considering a bright helmet. You really can see drivers doing a "double-take" when you are wearing such clothing. It's not exactly a fashion statement, but I'd rather be seen than fashionable.

So, next time you are out riding, give a little thought to the whole z-motion/x-motion thing. At the very least, it should help you to understand that the drivers who pull out in front of you are mostly not being vindictive or "out to get you". They are simply displaying basic human physiology.