by William Sommers
Fully Accredited Traffic Accident Reconstructionist (ACTAR #268)
Editor’s note: The following article was written for Gold Wing magazine, and bears reprinting.
“But officer, I…I didn’t see him. I just didn’t see him”. In my 30+ years of investigating accidents for two Southern California law enforcement agencies, as well as my own private practice, I have heard something like the previous statement a hundred times. I am an ACTAR accredited traffic accident reconstructionist, and a NHTSA certified police Drug Recognition Expert, and I have looked at all or part of over 10,000 accidents in the past 30 years. A recurring theme is a driver stating that he/she failed to see the other party.
Just what is this thing, “seeing”, anyway? Think about it for a minute. We all have said at some point or another that we either did, or did not see something, but can we actually describe what “seeing” is? There are several medical books on the subject, but traffic accident reconstructionists use a more simplistic approach to the subject. The reconstruction community, to a large extent, relies upon research done by Dr. Paul Olson of the University of Michigan. Dr. Olson’s book Forensic Aspects of Driver Perception and Response, along with his S.A.E. paper on the subject, is a corner stone for determining just what one “sees”.
Without getting technical, let’s consider the eye, and its nerve attachments, to be much like a simple digital camera. Light reflects off objects, is focused through a lens, and is pin-pointed onto a sensitive plane where the individual photons are converted into an image of what we, or the camera, is looking at. Since we are looking at visible light, and visible light is part of the electromagnetic spectrum, light must obey the same laws as radio, microwave, and other parts of the spectrum. One of these rules is the law of inverse proportions.
An example of this law is as follows: suppose at night you had a light source (headlight), and its beam was falling upon a guy walking 100 feet away. Let’s further assume that there’s now a gal walking 200 feet away and you want to see her with the same brightness that you saw the guy. Just doubling the number of headlights won’t do, you’d have to quadruple the number of headlights. Brightness diminishes as an inverse function of the square of the distance, so an object twice as far away would be only one-fourth as bright, three times as far away is just one-ninth as bright and four times as far away is one-sixteenth as bright.
Couple this with a dirty headlamp lens, dirty windshield, dirty glasses, and, heaven forbid, tinted eyeglass lenses or visor, and we have a recipe for disaster. The State of California even prohibits the wearing of the goggles some of our older drivers wear over their glasses. Vehicle Code §23120 specifically states that glasses with temple widths over ½ inch cannot be worn, so as to preserve lateral vision. The state is serious about people’s vision.
Most of the people reading this piece are Gold Wing operators, and many of us “Wingers” will never see 50 years of age again. This presents a problem with “seeing”. When we were a lot younger, our eyes would dilate to about 6.5 mm. The NHTSA uses a normal range of 2.5 mm to 6.5 mm in the DRE (Drug Recognition Expert) program. Some young, blond, blue eyed persons will dilate to over 7 `mm. When we reach 50 or so, that is no longer the case. Our eyes simply do not dilate as they used to.
I recently had Lasic surgery and, try as he would, my doctor could not dilate my eyes over 5.5 mm. This is typical of us who are older than about 50 years of age. What this means is that if your eyes used to open to their full 6.5 mm potential, they now admit only 71% of the light they used to admit. Have you found yourself carrying a paper over to a window to get more light or turning on more lights because you just couldn’t quite make out the text you were trying to read? This same problem will hold true if you are driving at night. Your eyes don’t open up as wide, and they don’t admit as much light, and you will miss some of the objects on the road.
Other terms we in our business use, and they sure apply to motorcycle riders, are : conspicuity, contrast, and expectation. Conspicuity is defined as “Those characteristics of an object or condition that determine the likelihood that it will come to the attention of the observer “ (Olson). He goes on to say that the fact that something is in the field of vision does not mean that it will be detected. The problem with conspicuity goes up as the surrounding information (clutter) goes up, such as signs, pedestrians, other traffic, and other items that would distract a driver.
We as riders must make ourselves as conspicuous as possible. We must also look for conspicuity in other things as we ride. Contrast is pretty much what its name implies. White on black, movement against a still background, these add up to contrast, and contrast adds to conspicuity.
Expectation is a condition a driver can assume to be the case or fact. Imagine, for a minute, that you are on a 70 mph freeway (75 for Arizonians). Would you expect the traffic around you to be going at about that rate? Sure, there will be some speeders, but would youexpect to see a vehicle stopped dead on the road in front of you? Would you expect to see a vehicle moving at 10 or 15 MPH on the road ahead of you? Of course not, and that leads us to another part of “seeing”. If an object is of a certain size when you perceive it, it will double in size as you get to a point halfway to the object. It will double in size again as that distance is cut in half. If you are not expecting to see a car stopped in front of you, some time may elapse before you realize, “Hey, this thing is not moving”. If you have your 50+ eyes, it is dark, you have tinted lenses, and a dirty headlamp and windshield, you may not have enough time to avoid a collision, whether you are driving a car or your motorcycle.
Normal perception and reaction time is generally thought of as being about 1.5 seconds for non-anticipatory response. Multiply your speed by 2.2 and this will give you the distance you need at that speed just to get your foot on the brake, but not yet begin the braking process. 30 MPH is 66 feet, 50 MPH is 110 feet, and so on. Central Nervous System depressants really mess with perception and reaction. One of the most used (abused) CNS depressants is Ethyl Alcohol. Everybody knows not to drink and drive, and not to drive when using tranquilizers and other such medications, but I will bet each and everyone of us has driven after using Diphenhydramine Hydrochloride. This is the sleep aid found in night-time pain killers and is used for colds, allergies, motion sickness, insomnia, and Parkinson’s Disease. Another name for it is Benadryl©. This medication is grossly abused, because people just do not know how powerful a CNS depressant it is. A test was done in Iowa where a number of test subjects were dosed to .10% blood alcohol, and a battery of tests were done to determine their impairment. The subjects were sent home and, after all the alcohol was gone from their systems, they were dosed to a therapeutic level of Diphenhydramine Hydrochloride and tested again.
A majority of the test subjects did more poorly with the over-the-counter drug than they did with the alcohol.
You can now understand that “seeing” is comprised of several components. We cannot control what other drivers see or do, except to keep our lighting in working order, to wear clothing that reflects, rather than absorbs light, and be alert to their movements. We can, however, keep our own equipment in peak operating shape, and we can realize our own strong, and not-so-strong points. If we need some kind of lens to reduce glare, don’t use sunglasses, as they will reduce the level of all of the light entering the eye. I have found that the amber lens used by shooters reduces the night-time glare (I have had some trouble with glare after the eye surgery), and it brightens up the scene to a point quite acceptable to good vision. I have realized that I’m not a kid anymore and, while I want to ride my bike as long as the good Lord will let me, I will modify my operation to fit the abilities I have or no longer have. Vanity is out the window here; this guy is not going to try to leap tall buildings in a single bound. I’ll just get on my bike and ride it. I hope that you will “see” that we can control to a large extent what, and how, we perceive things on the road and learn to make the proper adjustments…Ride safe.