Review of: Sorton, Alex, and Thomas Walsh: Bicycle Stress Level as a Tool To Evaluate Urban and Suburban Bicycle Compatibility; Transportation Research Record 1438

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1 Summary of Study

This is a starting attempt to rate roadways for cycling compatibility. The method is simple. Three primary variables are used: curb lane traffic volume, speed of motor vehicles, and curb lane width (other variables might later be added: commercial driveway frequency, parking turnover, percentage of heavy vehicles). Each variable is rated on a scale of 1 to 5. Curb lane traffic volume is rated linearly between 50 and 450 vehicles per hour. Curb lane width is rated linearly inverse between 10 and 15 feet (3.3 - 4.6 m). Motor vehicle speed is rated approximately linearly between 25 and 45 mph (40 - 75 kph). The range for each variable was selected according, approximately, to the minimum and maximum experienced in practice. The final score is the average of the three.

Obviously the final score can range between 1 and 5 inclusive. The score is related to characteristics of cyclists according to the following schedule.

1: Reasonably safe for all types of cyclists. (The study specifically excludes children of elementary-school ages.)

2: Can accommodate experienced and casual cyclists, may need altering to fit youth cyclists.

3: Experienced cyclists, casual cyclists if "compensating condition" is present.

4: Needs altering or compensating conditions even for experienced cyclists, not recommended for casual or youth cyclists.

5: May not be suitable for cycling.

The authors tested the system by showing video recordings of known conditions to groups of cyclists who were individually classified as experienced, casual, or youth. Each cyclist was asked to rate one factor at each viewing, giving 1 for being very comfortable and 5 for not wanting to ride with this condition under any circumstances. The scores given by all the cyclists of each class were combined and the linear regression calculated and compared to that given by the assumed rating system. For all three factors, the test cyclists rated the change in stress as the factor varied as considerably less than was used in the initial system. As one would expect, the experienced cyclists accepted more intense conditions for equal stress than did either the casual or the youth cyclists. The R-squared correlation values ran from 0.94 to 0.13, with strongest correlation for traffic volume, somewhat less for vehicle speed, and very poor for lane width.

2 Comments on Study

2.1 Improper relationships between variables

The suitability classification system does not properly consider the relationships between accident rate, cyclist skills, type of cyclist, and stress.

2.1.1 Accident rate versus specified conditions

The suitability classification system starts by saying that level 1 conditions are "reasonably safe for all types of cyclists," and progresses to level 5 conditions which are described as "may not be suitable for bicycle use." The implication is that the accident rate increases as the severity of the specified conditions increases, becoming unacceptably high for condition 5. However, we know that only a very small portion of accidents to cyclists are caused by motor traffic from behind, which is the only condition considered. There is no known relationship that allows us to predict total accident rate from merely the three factors that this study considers.

2.1.2 Required skills versus specified conditions

The suitability classification system specifically states that there is a relationship between the specified conditions and the skills that are required of cyclists. It states that "the on-street bicycling skill level of experienced bicyclists allows them to use the most direct and convenient routes, which often are the arterial or collector streets." This clearly distinguishes two kinds of characteristics. It says that arterial and collector streets require particular skills that are not needed on residential streets, and it says that experienced cyclists possess these skills.

However, the study does not specify those skills; all it considers are the conditions of motor traffic volume and speed and outside lane width. I know of no study that shows that increases in the intensity of these factors, singly or together, demand new skills of cyclists. Rather than that, we know that safe cycling requires that the cyclist exercise all of the five basic traffic skills, and that multi-lane roads require that the cyclist be somewhat better than is required on two-lane roads.

Instead of using that knowledge, the study rates roads according to conditions that have no reasonable connection with level of skill required. The only skill that is required to stay out of the way of motor traffic from behind is that of riding in a straight line near the right-hand edge of the roadway. That is the simplest traffic skill that exists and even elementary-school children, who are so unskilled that they this study excludes them, should be able to practice it.

2.1.3 Type of cyclist versus specified conditions

The study specifically classifies cyclists into secondary-school, casual (recreation, utility, shopping, etc.) and experienced (commuting, touring and recreation). This sounds as though it is a classification by trip purpose. That is, it distinguishes shopping trips from work or school commuting trips, or at least it distinguishes the cyclists who make such trips. I know of no study showing that these types of trips require different skills, or take place under different circumstances, or are taken by cyclists with different skills or levels of experience. Therefore, the classification of trip purpose by skill level is inaccurate. The explicit inclusion of skill levels does not fit the facts, as described above.

However, in addition to the level of skill supposedly attained by experienced cyclists, the study describes preferences, saying that "casual cyclists tend to give high priority to avoiding congested, heavily trafficked streets." If this is a study in preferences, then it should say so explicitly. If that is what it is, then all that it demonstrates is that those cyclists who don't like to use heavily trafficked streets do not like traffic.

2.2 Are Different Accident Rates Acceptable for Different Cyclists?

The only accident types that vary according to the motor traffic volume, speed, and width of outside lane are those in which the cyclist is hit from behind. Consider the difference between a high volume curb lane and a low volume curb lane. Presumably, the rate of accidents of this type varies according to the traffic volume. That is the assumption of this kind of study, and it is the most reasonable assumption given the absence of better data. The only action that the cyclist can take to avoid this kind of accident is to ride in a straight line; so long as the cyclist does not swerve in front of overtaking traffic, this kind of accident is purely the fault of the motorist. As is pointed out elsewhere, the skill of riding in a straight line is the most elementary traffic skill of all.

However, the study explicitly says that high-volume streets are acceptable for use by experienced cyclists but not for casual or secondary-school cyclists. This is equivalent to saying that higher accident rates are acceptable for experienced cyclists than are acceptable for casual cyclists. What is the justification for such a distinction? Why should society accept higher accident rates for experienced cyclists than for inexperienced cyclists? That is the opposite of what we find in practically all other fields, where society reluctantly accepts a higher accident rate for beginners than for experienced operators.

If the rating system is intended to be a surrogate for accident rate, then it needs to consider the causes of accidents and the system that is devised to do this must be calibrated against valid accident data. Sorton and Thomas have attempted neither of these activities. Therefore, all statements about safety or suitability that reflect or imply safety must be removed.

2.3 Difference Between Initial Estimates and Ratings By Cyclists

Perhaps the rating system is not intended to rate either safety or skill. After all, Sorton calls this a stress-rating system. So what is it measuring?

Or what would it be measuring if it was recalibrated in the light of the difference between the evaluations of the cyclists and the initial estimates? The most important finding is that all the ratings given by the viewers attributed much less increase in stress as the conditions intensified than was predicted by the initial estimates. The difference is least according to volume. Where the initial estimate was a total change in stress produced by change in volume of 4.5 units, the rated change was 3 units. For motor traffic speed, where the total estimated change in stress was 4 units, the rated change was only 1.5 units. For lane width, for the estimated total change in stress of 4 units, the rated change was 1 unit.

Sorton and Walsh write that the initial estimates were "extrapolated from transportation engineering literature covering motor vehicles and then related to the bicycle stress level process. (The logic behind this extrapolation is that if there are problems for motor vehicles, these will be bigger problems for bicycles.)"

This is not valid logic. The operation of overtaking motor traffic has little effect on the operation of bicycles until the cyclist needs to change lanes, and then the primary consideration is length of gap available, which for streets with heavy traffic is determined more by the location and timing of traffic signals than by the traffic volume itself. The lane width has some effect, because narrow lanes require the cyclist to ride a straighter line with less margin, but that effect occurs regardless of traffic volume.

The actual initial estimates were made using the typical range of actual values. That is, maximum lane volume achievable on conventional streets ranges between 450 and 800 vehicles per hour, depending on traffic signal operation. Therefore, Sorton set 450 vphpl as stress level 5. Similarly, there are typical ranges for outside lane widths and for motor vehicle speeds. Sorton set the most intense condition as stress level 5.

The ratings made by the cyclists viewing the videos showed that they attributed much less stress to changes in the conditions than Sorton's initial estimates. Surely, this indicates that these factors are not all important and that other factors must be considered.

2.4 Measuring Emotions

Even if the rating system is accepted at its face value, what is being measured? Sorton and Walsh understand that they are measuring a subjective emotion, because they suggest further research to determine whether cyclists from other cities than Madison, Wisconsin, give the same or different ratings for the same videos that were made and viewed in Madison. They suggest that "it may be that bicycle stress level depends on the population size of urbanized areas."

Emotional data will change with circumstances. Sorton's data demonstrate that the effect varies with experience. Therefore it probably does change with location, because different locations provide different experiences. We can presume that it is likely to change with time and even with political circumstances. This is not so far-fetched, since the emotion that is being measured is fear of motor traffic from behind, a fear that has been largely created by the motoring establishment and which is embodied in the measuring system itself. We know that this fear has very little bearing on the cyclist accident rate or on the skills required of cyclists. Why then should we consider it at all?

3 Conclusions

There is a great difference between studying a phenomenon and making recommendations for policy. All knowledge is valuable and it is not appropriate to question the motives of those who seek it. However, when that knowledge is bound up with recommendations, the motives of those who make them and the results of their recommendations should be assessed. The Sorton-Walsh study calls itself a method for assessing the cycling suitability of roads rather than a study of the emotions of different groups of the public; it must be evaluated with its intended purpose in mind.

3.1 Regarding Propensity to Cycle

One reason why we should study the fear of overtaking motor traffic is that it may be an important factor in determining whether a person takes up cycling transportation. If public policy holds that cycling transportation should be encouraged, then we need to consider ways to attract people to using it. If fear of overtaking traffic prevents people from starting to use cycling transportation, then we should consider what to do about this fear.

Sorton and Walsh's study presents one solution to the problem: falsely assume and falsely state that the fear reflects actual danger and reflects the level of skill needed to prevent accidents, and rate streets according to the degree of fear that inexperienced people feel about them. That has the advantage of not having to change people's opinions, but it has the disadvantage of perpetuating dangerous and harmful falsehoods.

The falsehood is the supersitition that the dangers of cycling are those of motor traffic from behind. This fear of overtaking traffic tells people not to ride at all because they are using the roads that belong to cars. It tells those who decide to ride despite the dangers of which they have been told that their prime need when cycling is to stay out of the way of the cars that are using the roads. This is the cyclist inferiority phobia. It is absurd to expect that a population that believes that these superstitions are physical laws will develop much cycling transportation wheh it has motoring available to it, and it is very likely that many of those in such a population who do choose to ride will do so incompetently. The resulting cycling transportation will be biased to short distance, slow speed, and inefficient cycling with low social standing.

This is of course the perpetuation of the present American system, in which there is very little cycling transportation, which is done by only a very small portion of the population, while those few who perform the bulk of it are those who have largely managed to overcome the general public superstition about cycling in traffic.

3.2 Regarding Public Policy About Cycling Facilities

Sorton and Walsh describe their purpose by writing that the cycling suitability of streets should be assessed when "developing a bicycle network to arrive at sound decisions on the appropriate locations of bicycle usage." In other words, either the public should be directed to use streets that have low ratings by the Sorton-Walsh standard or streets that provide desired routes should be changed to attain low ratings. In general, we have seen more attempts to direct cyclists than to change the road characteristics.

It is obvious that one result of such a policy is to direct cyclists away from the roads most used by motorists. Regardless of the effect on cyclists, that is a result that is desired by motorists. Therefore, the recommendation should be evaluated with that result in mind. If the recommendation makes little sense for cyclists, then it is reasonable to conclude even more strongly that pleasing motorists is a prime motive for the recommendation.

What benefit does the recommendation provide for cyclists? Sorton and Walsh do not provide any, saying only that "a procedure is needed that satisfactorily explains the effects of traffic volume, speed, and curb lane width on the different types of bicyclist." Hence we must look elsewhere for the supposed benefit. The typical argument is that cyclists do not know the best routes to take and need to be directed to them. However, we do not do this for motorists, except in a very general way. For motorists we provide destination signs and through route number signs, which assist strangers in the area to reach particular destinations or to travel through the area and, to some extent, we hope that these will channel through traffic away from residential streets. However, we do not expect that local motorists with local destinations will be directed by these route signs. We expect these persons to discover and to use, without other direction, the best routes for their particular purposes, whether or not these are the signed routes. There is no obvious reason why cyclists require a different service; indeed, since few cyclists travel very far, it is more likely that a cyclist will have a good knowledge of the streets within his smaller range of activity than does a motorist with his larger range. Therefore, this argument does not explain either the need or the desire.

It is argued that few of the people who might cycle actually know much about the streets that they might cycle on. Therefore, so the argument goes, they need to be told. That is no answer; it merely raises the question of why we need to tell them. These people are not children who are being let out into the world for the first time; they have traveled around their own areas by walking and driving, at least as passengers and probably by being drivers. All they have to do is to get out and try the different routes that they already know, and decide which they prefer. The whole argument is utterly foolish, but many people make it and public policy is based on it.

When the argument is investigated, its base is that the roads are so generally dangerous for cyclists and riding in traffic requires such an elite level of skill, that people who prospect for safe routes are too likely to be killed or injured before they find one. That argument is false in fact and the recommended method of designating safe routes according to the conditions of overtaking traffic is a false recommendation for a false policy. That is, the roads are not generally particularly dangerous for cyclists and the dangers that do exist are not defined by the conditions of overtaking motor traffic.

Sometimes this argument is redefined to say that even though roads with heavy traffic are not particularly dangerous, it is sufficient that those who do not cycle believe that they are. In other words, this version of the argument goes beyond the tacit, unquestioned, but false, assumptions of the Sorton-Walsh method and recommends lying to the public with malice aforethought to achieve some objective other than the good of the cycling public.

3.3 The Sorton & Walsh Study as a Basis for Cycling Policy

3.3.1 Sorton and Walsh's recommendations have no scientific justification

Sorton and Walsh advance no reasons for believing that their procedure provides an accurate measurement of anything. If it measures anything at all, it measures a fear in an abstract setting according to an intellectual kind of consideration. That is, it asks "How frightened would you feel if you were to cycle on a street with these conditions of overtaking traffic?" No psychologist would consider the study by Sorton and Walsh a reasonable study of fear. I think that we need to study this fear, but we need to study it in a way that reflects psychological knowledge and technique. I think that we need to study this fear because it is a prime factor in our problems with cycling transportation. Once we know more about it, we may be able to devise better ways of dealing with it.

Sorton and Walsh advance no reasons for believing that following their recommendations is good public policy. They tacitly assume that the prevalence of such arguments justifies their recommendations. However, the arguments that have been given for following such recommendations have been shown to be, at best, false and, at worst, deliberate lies to suit either, or both, anti-motoring and motorist-comforting agendas.

We need a sound policy for cycling transportation, and such a policy has to consider the fear that the general public has about cycling in traffic. However, the Sorton-Walsh recommendations for dealing with that fear have no scientific basis for being part of that policy. Following their recommendations would not only be scientifically dishonest, but it is poor policy because it gives official support to false fears about cycling.

3.3.2 The seductive nature of the Sorton-Walsh recommendations

There are several reasons why the average person finds the Sorton-Walsh recommendations to be psychologically seductive. The most basic reason is that he incorrectly believes that the prime danger to cyclists is the motor traffic from behind. Since he believes this, the thought that Sorton and Walsh may be wrong doesn't cross his mind. More than mere intellectual quiescence, any program that questions the basis for Sorton and Walsh's recommendations threatens the belief on which he relies for his own safety. Furthermore, since he knows that he cannot do anything to avoid the great danger of being hit from behind, he must consider that those who ride in traffic are either risk-taking fools or possess some super-human ability to bounce cars off their backs. This means that safe cycling in traffic is not a matter of skill and judgement but requires magic powers that are unavailable to ordinary mortals. For most Americans, these are psychologically compelling motives.

There are other reasons why the Sorton-Walsh recommendations are easy to believe. The program promises safe cycling without the cyclist having to do anything or take any responsibility. The program promises motorists (and most American voters are motorists first and are very unlikely to be transportational cyclists at all) to get cyclists out of their way on the roads that they most want to use. The program does not threaten anyone with becoming a cyclist or even considering becoming one; if it persuades someone else to become a cyclist, that's all to the good, and it will keep him off the roads that I want to use.

There is also the pragmatic argument that it is often easier to change physical conditions than to change people's behavior. However, the conditions under which this principle applies are not present here. The changes in conditions (some designated bicycle routes, some widening of curb lanes) cannot compel people to cycle. All they can do is to persuade, but at the same time the policy that justifies these changes is based on, and strengthens, the false superstition that most of the roads are too dangerous for cycling and that individual cyclists cannot do anything to improve their chances. In short, a policy based on the Sorton-Walsh recommendations strengthens the cyclist-inferiority superstition, which is exactly the incorrect policy. Given these mutually opposed forces, any cycling transportation that is generated will be less than would naturally occur if cyclists understood the truth, and will tend to undercut and denigrate the position of those who, today, are doing the bulk of the cycling transportation.

In summary, there are many reasons why the Sorton-Walsh recommendations exert powerful psychological attraction, but none of those reasons is scientifically justifiable.

3.3.3 The Responsibility of the Bicycling Committee of the Transportation Research Board

The Sorton and Walsh paper was published by the Committee on Bicycling and Bicycle Facilities of the Transportation Research Board, an arm of the National Academy of Sciences. Were I still reviewing papers for that committee, I would have recommended rejection for the reasons stated herein: there are too many obvious scientific errors.

Possibly, publication of the research data would be justified as an analysis of public opinion about cycling, provided that that was investigated in a manner suitable for such a subject. Such a publication would necessarily have to include an evaluation of the errors in such opinion.

The Bicycling Committee of the Transportation Research Board is supposed to be composed of those who are most competent in the nation regarding knowledge of cycling transportation. Unfortunately, the committee has never lived up to that supposition. The committee of fifteen years ago, when I knew it well, would have accepted this paper, just as the present committee has. Rather than basing its acceptances on scientific accuracy, the committee has too frequently judged according to the degree to which a paper agrees with the superstitions of the majority of its members and the corresponding policies of the governmental organizations in which many of them work.

4 A proper policy for cycling transportation

In my opinion, honesty would be a much better policy. That is, to teach people what is actually known about cycling. We know the skills that are required for cycling in traffic and we have sufficiently accurate knowledge about the dangers of cycling and how to handle many of them. The skills and conditions are generally those that occur when cyclists act and are treated as drivers of vehicles. We know how to teach these lawful skills to those who want to learn them. We have generally adequate traffic laws that require other road users to operate properly with regard to cyclists. These conditions are sufficiently well met throughout the nation that those who choose to cycle properly can generally do so. We do have problems with the road system, but they are generally local and are not systematic, and they would be much more easily solved if the public accepted that cyclists are drivers of vehicles.

We need to face and overcome our problem that the public has been misled about cycling for decades. Cyclists are not inferior to motorists, they are not at great danger when they cycle properly, and they fare best when they act and are treated as drivers of vehicles. To correct this psychological untruth will be harder than making easy, but false, promises that changes to facilities will make cycling safe. However, telling the truth and acting on it is the only way that we can reasonably persuade more people to perform cycling transportation in distributed cities such as we have today.

Certainly, we need a systematic way for parents and guardians to limit the locations where their children may cycle, but that needs to be done on the basis of the skills of each individual child rather than on factors, such as Sorton's three, that have little bearing on the ability of the child to operate properly in reasonable safety.

It is a truism to say that over the long run, truth is a far better guide than falsehood. With truthful knowledge about cycling, we can expect a reasonable amount of cycling transportation done in the best ways. That is the only kind of cycling transportation that can compete against the automobile in today's distributed cities.

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