Home Experience Services Contact Us Seminars Attorney's Guide to Perception Resources
Bicyclists: Read This To Save Your Life1

Marc Green

I have investigated many vehicle-bicycle collisions during my time as a human factors expert in collision analysis. I have also read many bicycle discussion forums and overheard bicyclists' conversations at fast food restaurants. There is apparently a major discrepancy between what bicyclists believe causes most vehicle-bicycle collisions and what actually causes most vehicle-bicycle collisions. If you are a bicyclist, this discrepancy and your faulty beliefs could get you killed.

Before starting, a little house cleaning. Bicyclists apparently fall into two general groups. One group rides a bicycle based on some "paradise lost", Mr. Natural, anti-capitalist, blah, blah, blah ideology. This element of society likes to turn everything into an ideological issue. They make statements like, "Bicycles have the potential to transform our society into one that respects all nature, including our fellow humans" or that cars " encourage its owner to get fat and unhealthy" and "even if they never crashed", they still require "obliging healthy and harmless walkers to yield priority to inactive and polluting drivers". Or they have a chip on their shoulder with an "I'll do whatever I want and don't you dare tell me what to do" sense of entitlement. Others like to ride on the edge for the thrill of danger. For some, it is a form of agressive behavior, designed to provoke. If you are one of these, read no further. As I have learned, you are beyond hope and beyond reason.

If you see vehicle-bicycle collisions as a safety, rather than an ideological, issue, then both my experience as an accident investigator and the scientific research evidence on bicycle crashes can help you stay alive and unharmed. I can tell you up front, however, that you probably won't like much of what I am going say - that the primary responsibility falls on you.

Vehicle-bicycle collisions typically occur because the driver does not see the bicycle. Understanding why this occurs is your best bet to stay alive. If you think this usually occurs because drivers are reckless or aren't looking where they are going, then you are wrong. Certainly, a collision can (and does) occur because a driver is distracted, speeding, intoxicated, etc., but these are the exceptions and not the rule. In sum, drivers generally do not see bicyclists for one or more of the following reasons:

1.         The driver's attention is focused on avoiding collisions with other vehicles and pedestrians;

2.         The bicyclist has low visibility/conspicuity; and

3.         The bicyclist violates driver expectation;

The first problem cannot be fixed by drivers or by bicyclists. It is simply human nature. We all have limited attention, which we learn to deploy to avoid the biggest and most probable hazard. However, bicyclists can learn to anticipate and to avoid the most hazardous situations to some extent. The second two issues are problems over which drivers have no control, but which bicyclists can minimize. 

1. The driver's attention is focused on avoiding collisions with other vehicles

Recently, I had an experience which exemplifies the attention problem. I was making an afternoon trip to the supermarket and made a difficult right turn on to the street where it was located. I narrowly missed a bicyclist coming from my left. I had looked left, saw nothing, and looked right toward my direction of travel (i.e., looking where I was going). As I started to move, I glanced back left and noticed a bicyclist not far away. By the time it registered, I was well into my turn and blocking his path, so it was too late to do anything but continue forward. The bicyclist slowed, but then bicyclist followed me into the supermarket parking lot, stopped at my car and signaled me to lower my window.

He then went on a controlled rant saying that I had almost killed him because I was looking for cars and not bicycles and that I should be more careful. He said that he even had a front light, so I should have seen him.

I then did the worst thing that I could do to him. I agreed! He was exactly right. I had tuned my attention to look for cars and not bicycles. I could see that he was caught off guard and taken aback. He became more civil advised that I pay more attention to bicycles. I told him that after this incident, I would try to be more careful. Just then, a car came up behind us, and we had to move. He pedaled away.

Unfortunately, we didn't get the chance to finish our conversation. I would have told him a few facts of life. I might look more for bicycles for the rest of the day. Maybe even for a few days. Whatever my good intentions might be, however, human nature would take over in the long run. Bicycles are relatively rare in my part of town. Other vehicles are larger, more common and pose a much greater hazard to me. The basic fact is that telling people to pay attention is futile. Attentional tuning occurs largely outside of awareness. It simply was not going to include bicycles. (The "Think Bicycles" campaign now underway is a waste of effort.) I have my searched satisfied when my glance leftward had found no cars approaching in the lane that I was entering. You can't fool Mother Nature, or Human Nature for that matter. This is the way that we are designed.

Further, I would have explained that his little light wasn't going to make any difference in the daytime and that he shouldn't let it generate an overconfidence. I would have told him that he would be much better off getting a fluorescent yellow vest, but that he shouldn't bet his life on it.

This incident reflects the reality of being a driver. Scientific research has shown this reality in many, many studies. Even Ian Walker (1916), who is an extreme anti-car zealot, had to admit that his review of the research literature led to the following conclusion:

"to compensate for limited information-processing capacity, drivers form expectations of what they will encounter on the road and use these to guide their attention. These expectations often predict that only cars and other such vehicles will be encountered (which, statistically, is a reasonable assumption in many environments). As a result, drivers attend only to motor vehicles and regions of space in which motor vehicles are found... it is too demanding for drivers to attend to regions that might contain motor vehicles and regions that might contain VRUs." (Walker, 2016)

Even some bicycle advocates preach this reality. In the article "See and Be Seen", Cycling Tips also says "drivers of four-wheeled motorized vehicles are primarily looking out for other cars and trucks, not motorcyclists or cyclists."

The bottom line is that drivers may not see you for very good reasons. Never assume that you will be seen, even in daylight. Driving takes attention, and driving in heavy traffic takes almost all the driver's attention. This is an especially dangerous situation because the bicyclist may be moving faster than the traffic, which the driver is monitoring to determine what is happening. The bicycle then seems to come out of nowhere. It is very dangerous for bicyclists to start zipping between slow moving cars. Further, the most demanding driving task is the left-hand turn across traffic. Watch out for these situations, in particular. One study found that drivers intending to turn left spend almost all their attention monitoring traffic from the right and fail to see bicycles coming from the left.

2. The bicyclist has low visibility/conspicuity

For drivers to respond to a bicycle, it must be visible, conspicuous and recognizable. That is, the driver must sense that you are there, have his attention engaged and then recognize you are a bicycle and not some disembodied light.

I've read many crazy rationalizations by bicyclists for not wearing high-visibility clothing, but that's all they are - crazy rationalizations. (Forget about the moth effect. It happens, but it is very rare compared to collisions caused by lack of visibility.) Further, bicyclists, like pedestrians, drastically overestimate their visibility (Wood, Lacherez, Marszalek & King, 2009; Wood, Tyrrell, Marszalek, Lacherez & Carberry, 2013).

The great benefits of high visibility clothing have been repeatedly proven. A review of 42 research studies (Kwan & Mapstone, 2006/2015) found that bicyclists were much more detectable when wearing a fluorescent vest during the day and had lights at night. One nighttime study (Wood, Tyrrel, Marszalek, Lacherez, Carberry, Chu & King, 2010) found when bicyclists wore dark clothing, no older drivers (range 66-80) and only two percent of younger drivers (range 18-35) recognized bicyclists. Adding a retroreflective vest raised the percentages to about 25-30 percent of older and 60 percent of younger drivers. Adding retroreflectors to ankles and knees, creating "biological motion", further increased the percentages to 80% and 100%. Biological motion is the addition of moving points of light, such as the up-down motion of pedal reflectors, which make recognition easy for drivers. I highly recommend the retroreflective ankle bands that now available in many running stores. Several studies have show that recognition depends on the distribution of retroreflective material and not simply the amount (e.g., Cassidy, Brooks & Anderson, 2005). To see how moving points of light lead to instant recognition, view the video at http://www.michaelbach.de/ot/mot_biomot/index.html.

Real-world evidence confirms the safety benefits suggested by such research. For example, 6,800 bicyclists were randomly assigned to yellow retroreflective jacket and no jacket conditions (Lahrmann & Madsen, 2016). The jacket group had 48% fewer vehicle collisions. The actual effect was much bigger, moreover, because 37% of the jacket group collisions occurred when they were not wearing their jacket at the time of injury.

You might as well start wearing high-visibility clothing now. France already has laws requiring its use and similar legislation is being discussed all over the US and Europe. You cannot complain about drivers not seeing you when you make no attempt to optimize your visibility and conspicuity.

When it comes to conspicuity aids, such as lights, the basic rule is that "contrast is everything." Nothing is by itself is inherently visibly or conspicuity. Objects are only conspicuous when they differ from the background:

1. Bright object on a dark background (or vice versa);

2. Flashing/moving object on a steady background; and

3. Colored object on its complementary background (red on green, etc.)

One consequence of these basic rules is that any lights will be highly beneficial on dark streets, but they probably help much less in urban environments where there are many other background lights from building, cars, streetlamps, etc. and their reflections. Flashing lights are then better because they stand out from backgrounds of steady lights. However, it is difficult to localize single lights. Drivers may not be able to tell exactly where you are. Distance is especially hard to judge.

Worse, single lights do not help drivers recognize you. You must not only be visible but also recognizable. The single light on your bicycle might just be another meaningless bright point in a scene with other bright points from buildings, vehicles, mail box, etc. This is when retroreflective safety vests and biological motion are important - it makes you recognizable as a distinct object.

Even under the best of circumstances, however, these "sensory conspicuity" aids have only so-so potency. Research shows that they are most effective when the viewer is actively searching for them. When it is a matter of "just noticing" something unanticipated, they are less effective (e.g., Green, 2017). When a person is performing a familiar, routine task, then sensory conspicuity aids have even less effect. In these cases, "cognitive conspicuity", meaningfulness and expectation, determines whether an object is noticed. This leads to possibly the most important factor in a bicycle's not being seen - violated expectation.

3. The bicyclist violates driver expectation

I have read many articles written by bicyclists about safety. Some are very good. However, none tackles perhaps the fundamental problem. Bicyclists don't obey the law. Since drivers generally anticipate that other road objects to follow the rules, failure to obey the law violates expectation. Driving is based largely on expectation and violated expectation is sure to lead to disaster. In fact, the central doctrine of road design is "Positive Guidance" (Alexander & Lunenfeld, 1986), which is based on the tenet that roads and traffic patterns must be made consistent with driver expectation. It starts out by saying:

Driver expectancy is a key factor in driving task performance. It affects all aspects of driving, including pre-trip planning, hazard avoidance, lateral placement, speed control, road following, route following, and direction finding. It affects how drivers react to and handle information, how they make decisions, and how they translate their decisions into control actions and driving strategies."

Scientific studies of vehicle-bicycle collisions come to the same conclusion: crashes are most likely to occur when the bicyclist violates traffic rules (Gohl, Schneider, Stoll, Wisch & Nitsch, 2016) and comes from a when the bicycle is traveling inconsistent with normal traffic flow (Hunter, Pein & Stutts, 1995), generally an illegal direction.

There is a further consequence of all this illegal behavior - it antagonizes drivers. Drivers have to predict the behavior of other road users. The constant illegal behavior of bicyclists makes this very difficult and adds heavy burden to the driver. I know many drivers who absolutely hate bicyclists because of their illegal behavior and sense of entitlement. Drivers want to avoid vehicle-bicycle collisions almost as much as bicyclists do. They may not die, but they know that the legal consequences will almost make them wish they had. The presence of bicycles slows traffic and creates great stress for drivers, a stress that is increased by bicyclists' constant unpredictable zipping in and out of traffic, switching from streets to sidewalks,ignoring traffic controls etc.  In short, bicyclists make the driver's life much more difficult and compound the problem by seeming to believe that they are free to flaunt the law and by their frequent violent behavior of banging on cars - or worse. Is it any wonder that many drivers hate bicyclists?

Drivers don't think that they should be put at that risk by people with a sense of entitlement that they are above the law and morally superior. Drivers are not likely to show you much courtesy if you make life harder for them by not showing them any courtesy. Sharing the road means following the rules. This applies as much bicyclists as to drivers.  Given the inherent complexity and dangers in a road system that includes objects of such disparate sizes and speeds as trucks, cars, motorcycles, bicycles, and pedestrians, rules and courtesy are absolute necessities for making the system work. Pounding on the side of a car after a near miss will do nothing but make an enemy for all bicyclists.

The illegal behavior is abetted by other risky, drunken and distracted pedaling. When people think of such collision factors, they typically think of drivers. However, research shows that alcohol in pedestrians and bicyclists probably leads to more road deaths. For example, most people are unaware that about half of adult road pedestrian fatalities were drunk (BAC >0.08) at the time of the collisions. A drunken pedestrian is 3-8 times more likely to be killed by a sober driver than a sober pedestrian by a drunken driver. In other words, drunken walking is far more dangerous than drunken driving.

Although there are fewer data on bicyclists, drinking in bicyclists is common. The percent percentage of fatally injured bicyclists age 15/16 and up had a BAC above the legal limit for driving is 20 to 30 percent  (Li & Baker, 1994; Eichelberger, McCartt, & Cicchino, 2017). The rate of bicyclist fatalities who had been "drink pedaling" between 5 PM and 8 AM was 62 percent, with 41.6 percent having a BAC .05, the legal limit where the study was conducted (De Waard, Houwing, Lewis-Evans, Twisk, & Brookhuis, 2015). Alcohol also correlates with riskier bicyclist behavior and with a helmet use of 16.5%, compared to 43.2% for sober bicyclists (Sethi, Heyer, Wall, DiMaggio, Shinseki, Slaughter & Frangos, 2016).

Bicyclists distraction is also growing dramatically like pedestrian distraction. Listening to personal music devices causes more unsafe behavior in bicyclists (Terzano, 2013). This distraction translates into a higher collision probability (Ichikawaand Nakamara, 2008), at least for younger bicyclists Goldenbeld, Houtenbos, Ehlers & De Waard, 2012). Pulling into my driveway ten minutes ago I saw a high-speed bicyclist go by. He had one hand on the handle bar and was watching the screen of his phone that he held in his other hand. He was not watching where he was going. That was a recipe for disaster, both for him and for pedestrians crossing the road.

The opinions expressed above are not new or simply mine. The table below shows the steps suggested in an excellent recent article (Shilton, 2015) on improving bicyclist safety at night. The first five largely address the major causes of the collisions found in the research discussed above. Shilton also adds a sixth that it is would be wise to avoid major roads, where traffic is faster and conflicts are more probable and at night ride roads with more lighting. This is also good advice.

Safety Measure


1.      Assume No One Can See You

bicycles are not highly conspicuous

2.      Pick A Smart Outfit

wear reflective and retroreflective material

3.      Let There Be (Lots of) Lights

have front and taillights

4.      Illuminate Yourself to Look Human

use biological motion

5.      Follow Your Local Laws

have (bicycle) the lighting legally required

6.      Pick a Smarter, Not Shorter, Route

ride ones with less traffic or more lighting

7.      Be Where You Are Supposed To Be

follow the rules of the road

However, Shilton, and many of the otherwise best bicycle advocates, still refuse to address perhaps the most important issue, which I have added as a seventh. The first law of VRU safety is the same as the first rule of road design: obey traffic regulations and don't violate driver expectation. Drivers allocate attention based on task and expectation and nothing is ever going to change this. The factors that control attention, probability, and relevance, already work against bicyclists in many cases. Darting, ignoring traffic controls and taking paths outside of normal traffic flow compound the problems. There is nothing that drivers can do about this. There is plenty that bicyclists can.


I told you up front that you probably wouldn't like what I am going to say: forget about drivers because the responsibility for safety lies with you. The bottom line message is that you should focus on controlling what you can control. Bicyclists can complain about drivers not seeing them all they want. It won't make them any safer. You can't change drivers because human nature is the least mutable part of any system. On the other hand, you can control your likelihood of being seen and noticed by wearing high-visibility clothing and by having good lights and creating biological motion, by not darting through traffic and especially by obeying traffic control. If you don't start doing this, you may force authorities to start licensing bicycles as in Switzerland and imposing traffic fines and mandatory safety classes as in Manhattan. The best way to avoid government regulation is to take safety into your own hands. We all know much governments like to regulate if given any excuse.

Hardly a day goes by when I don't see a bicyclist traveling the wrong way down a one-way street, going back and forth from street to sidewalk and blowing through STOP signs and red lights. The research on this confirms personal experience that bicyclists simply ignore the law. Just a few weeks ago, I approached an intersection when a bicyclist on a crossing road with a steep downgrade blew through a stop sign at probably 30 mph. He made no attempt even to slow and could not possibly have seen me in time to avoid a collision. Fortunately for him, I had STOP sign in my direction, so I was slowing to halt. If the road were regulated as a two-way STOP rather than a 4-way, he would quite possibly be dead right now, and I would probably have been blamed.

Here's the bottom line. If you want to be treated like a street vehicle then you have to act like a street vehicle. That means complying with traffic regulations. Sure, not all drivers act perfectly, but you have no control over that. Sure, it is more work to come to a stop rather than to blow through the STOP sign. Well, safety never comes for free. It always creates inefficiency and cost that someone has to pay. If you aren't willing to pay the costs, wearing a helmet and high-visibility clothing, choosing longer but safer routes, and complying with traffic regulations, then you have no complaints. You made the choice to take the risk.


1Citations are not included here, but are available in Green, M. 2017, Roadway Human Factors: From Science To Application.

Other Topics
Personal Injury: Road Accidents
  • Is The Moth-Effect Real?
  • Human Error in Road Accidents
  • Reaction Time
  • Let's Get Real About Perception-Reaction Time
  • Why PRT Is Not Like Gravity
  • Vision in Older Drivers
  • Weather and Accidents: Rain & Fog
  • Accidents At Rail-Highway Crossings
  • Seeing Pedestrians At Night
  • Underride Accidents
  • Rear End Collision: Looming
  • Night Vision
  • Distracted Pedestrians
  • Failure To See
  • Perception-Reaction Time (PRT) Programs
  • Twilight (3.3 lux) As A visibility Criterion
  • Human Error And Fault Tolerance
  • Why Pedestrians Die
  • Bicyclists! Read This To Save Your Life
  • Bicyclists! Read This To Save Your Life
  • Personal Injury: Warnings & Product Defects
  • Warnings and Warning Labels
  • Warning Effectiveness Checklist
  • The Psychology of Warnings
  • Drugs, Adverse Effects & Warnings
  • Are Warnings Effective?
  • Human Error Vs. Design Error
  • Product Misuse And "Affordances"
  • Safety Hierarchy: Design Vs. Warning
  • Thinking Like A Human Factors Expert
  • Personal Injury: Other
  • Diving Accidents in Pools
  • Falls Down Steps
  • Medical Error
  • Computer & Medical Error
  • Criminal & Police
  • Errors in Eyewitness Identifications
  • Perceptual Error in Police Shootings
  • Eyewitness Memory Is Unreliable
  • Human Factors In Forensic Evidence
  • Intellectual Property
  • "Any Fool Can See The Trademarks Are Different"
  • Measuring Confusion For Intellectual Property
  • Color in Trademark and Tradedress Disputes
  • Visual Human Factors
  • 33 Reasons For Not Seeing
  • Seeing Color
  • Determining Visibility
  • "Inattentional Blindness" & Conspicuity
  • Computer animation has perceptual limitations
  • Photographs vs. Reality
  • The Six Laws Of Attention
  • What is "inattention?"

  • | Home | Experience | Services | Contact Us  | Seminars/CLE | Attorney's Guide  | Resources |

    Send this link to someone

    Copyright © 2013 Marc Green, Phd
    Home Page:
    Contact Us