John Gwynne, PhD. Pacific Science & Engineering Group, 6310 Greenwich Drive, Suite 200, San Diego CA 92122; Marvin Levy, PhD., National Highway Traffic Safety Admin., 400 Seventh St. SW, Washington DC 20590

Saturday, 16 October, 1993

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This review refers only to bicyclist part.

Review by John Forester

Well, now that you are getting down to this subject, you should recognize that cyclists, at least when on the roadway, are drivers of vehicles. Therefore, you need to discuss both the interaction of motorists with cyclists who are acting as drivers and the interaction of motorists with cyclists who are not acting as drivers. This is probably the most important consideration that you could impart to authors of instructional books for motorists. You could, of course, call them all drivers, but you need some means of identifying the three groups. Therefore, call motorists motorists, call cyclists bicyclists, and call cyclists on the sidewalk sidewalk bicyclists. I divide my comments in the following into two categories, those that apply to cyclists who are not acting as drivers and those that apply to cyclists who are acting as drivers. The material in boldface type is my suggestion as to the exact wording of the subject material.


Driver Fails to Detect Bicyclist

The first group of accidents discussed is defined in an absurd way: Driver Fails to Detect Bicyclist. Of course he didn't, but that definition applies to many other situations, and provides the wrong signal. It also misleads the prospective authors of the documents that are desired. I take it that the situation discussed has to do with the motorist entering a driveway. It also applies, although not shown, to the motorist exiting a driveway. I suggest the following:


Many bicyclists ride on sidewalks. When they do so they don't act like either pedestrians or drivers. They are too fast for pedestrians and follow none of the rules for drivers. Whenever you are entering or leaving a driveway or an alley that crosses a sidewalk, first look both ways for fast bicyclists on the sidewalk. Let them go past before crossing the sidewalk.

(Bicyclist) Midblock Rideout

There is little point in trying to get motorists to prevent this type of accident; it happens too fast for the motorist to do anything about it. It is unreasonable to expect motorists to slow down behind every bicyclist they 1111111see cycling on a sidewalk just in case that bicyclist may swerve into the roadway at any driveway. The only useful instruction is to drive as far away from the curb as is otherwise reasonable, and this should be a driving habit that is always followed whether or not a bicyclist is seen on the sidewalk.

Bicyclist Rides Into or is Caught in Intersection

These are two entirely different types of accidents and should not be confounded into one confusing type. There is (1) Bicyclist Violates Stop Sign or Traffic Signal and (2) Bicyclist Is Caught On The Yellow Signal Phase. (1) is an unlawful action by the bicyclist, (2) is a lawful incident that is caused by poor traffic signal timing.



Bicyclists often violate stops signs and sometimes violate traffic signals. If you see that a bicyclist approaching an intersection has decided not to stop when required by a stop sign or traffic signal, making you likely to hit him, apply your brakes hard and hope that you stop in time.

There is no other useful instruction that you can give to motorists. They aren't about to slow down whenever they see a cyclist near a stop sign or traffic signal, nor should we expect them to do so.

Driver Overtakes Bicyclist

The situation discussed has nothing to do with the motorist overtaking a bicyclist. The accident type is:


Bicyclists often unlawfully swerve about on the roadway. If other traffic conditions permit, when overtaking a bicyclist give him as much room to swerve as you can. If the bicyclist does swerve in front of you, apply your brakes hard and hope that you stop in time.

Bicyclist Approaches Head-On

The situation discussed is probably more likely the wrong way bicyclist who causes about 30% of car-bike collisions.


Bicyclists often ride unlawfully on the wrong side of the road. This puts them unexpectedly in front of motorists when motorists turn, and sometimes when motorists are going straight. When making turns, try to look along the wrong side of the street for approaching bicyclists. If you see one coming on the wrong side of the street, wait for him to pass.

I suggest that one of the most important thoughts to impart at this point in the discussion is that unlawful cyclists cause over half of the car-bike collisions that occur.


You can see from this discussion that you as a motorist can do only a little to prevent crashes between unlawful bicyclists and your car. You should do all that you reasonably can, but the collision is still likely to happen. Applying your brakes hard to get your speed down before the crash will lessen the injuries to the bicyclist (and the damage to your car). Over half of the crashes between cars and bicycles are caused by the bicyclist disobeying the rules of the road for drivers of vehicles. The very best method of preventing these crashes is to teach bicyclists to ride properly, like drivers of vehicles. Then you won't be faced with these nasty situations.



When bicyclists act like drivers of vehicles motorists are not faced with unexpected situations that result in collisions and are difficult to avoid. Motorists have only to be careful to obey the normal driving rules of the road. The following instructions simply encourage that behavior and point out the situations in which motorists have to be careful to look for bicyclists.

The situation in which the bicyclist is caught in the intersection at the end of a yellow signal phase is the most frequent cause of car-bike collisions that are caused by deficiencies in the highway system.


Bicyclists often get caught in wide intersections with traffic signals at the end of their yellow light. They may be hidden by other traffic that is waiting for a new green. If the signal turns green for you, particularly if you are still moving while traffic in other lanes is still stopped, slow or stop until you see that the intersection is empty.


The crash when a motorist turns left in front of an oncoming bicyclist is the most frequent type of motorist-caused car-bike collision. Whenever turning left, look carefully for an oncoming bicyclist and wait for him to pass before turning left.


The crash when a motorist turns right in front of a cyclist who is going straight is a frequent cause of car-bike collisions. When you intend to make a right turn and there is a bicyclist near you, you must decide whether to turn in front of him or behind him. Decide to overtake the bicyclist and turn right ahead of him only if you will be a long way ahead of him. If you can't get a long way ahead of the bicyclist, then wait and turn behind him. Either way, move right to next to the curb long before you make the turn. That gives the bicyclist the chance to avoid your turn if you do it wrong.

If you are moving slowly in traffic and decide to turn right, look behind you to see whether there is a bicyclist there. In any case, make it your habit to move right slowly to close to the curb long before you make the turn to give any bicyclist the chance to avoid your turn if you do it wrong.


Overtaking a bicyclist is the most frequent movement that a motorist makes about bicyclists. The rule is simple: you must overtake only when it is safe to do so, just as when you are overtaking a car or truck. See that there is sufficient width for you to clear the bicyclist safely. At low speeds a three-foot clearance is sufficient; at higher speeds five feet is much better. If the road is so narrow that you must move to the left to get past the bicyclist, see that there is sufficient clear distance ahead for you to get well ahead of the bicyclist before you have to return to your normal position on the roadway.


Large vehicles driven fast generate considerable air turbulence that pushes bicyclists first to one side and then the other. When the vehicle is traveling against the wind this effect is stronger. When the wind is blowing across the path of the vehicle the vehicle first cuts off the side wind and then allows it to resume, which has much the same effect. To reduce the effect of air turbulence the American Trucking Association recommends giving 5 feet of clearance at 50 mph and an additional foot for every 10 miles an hour above that.

Long vehicles that have to start their right turns a long way away from the curb may cut off bicyclists on their right. Drivers intending to turn right should turn on their turn signals well in advance. They should slow down behind any bicyclists they see and let them go ahead before making the turn. They should look carefully in the right-hand rear view mirror for bicyclists before actually making the turn. They should make the turn at low speed to give any bicyclists (or pedestrians) who may be there a chance to avoid the truck.

It has taken me only two hours to do this because I know the subject. If I had been asked I might even have done this for free. My point is that if the government had asked the people who know the subject (there are several of us and the government knows who we are and with what organizations we are associated), it would have received good work much faster. People who are so unfamiliar with the subject that they have to make a research project of looking up a few facts (mistakenly thinking that those were the most relevant) in government documents cannot be expected to produce good results on their first try. I heard about this project only by accident and only because review copies of the completed (sic) document were being circulated. If, on the other hand, the government wants to avoid using the knowledge of those who know the subject, presumably because that knowledge doesn't agree with the popular feeling, then it stands convicted out of its own mouth. As it is, those who know the subject can participate only by complaining about how badly the work has been done, and that only by accidentally hearing about it. Too often, we have been completely left out of the loop and have had to publish devastating criticisms of what has been done.


Respectfully submitted,


John Forester


cc John Allen

Gil Clark

Susan Jones

June Thaden

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