I write here in response to an online article in the Grist blog, which addresses the concept of “safety in numbers” among cyclists and pedestrians. As is all too common, the article takes this phenomenon for granted, and ascribes it entirely to changes in behavior of motorists. There is no mention of changes in behavior of cyclists and pedestrians themselves.
The concept of “safety in numbers” is often applied to animal behavior, and a couple of examples might be useful. Here’s one from the University of Rhode Island Sea Grant program:
A potential predator hunting for a meal might become confused by the closely spaced school, which can give the impression of one vast and frightening fish. Additionally, there is the concept of “safety in numbers”—a predator cannot consume an unlimited quantity of prey. The sheer number of fish in a school allows species to hide behind each other, thus confusing a predator by the alteration of shapes and colors presented as the school swims along. Of course, those on the outside edges of the school are more likely to be eaten than those in the center.
Here’s a video of such behavior.
A herd of animals may actively defend its members, as shown in this astonishing video.
In warfare also, there are issues of safety in numbers, discussed in terms of “swarm warfare“. In some cases, the opposite tactic is applied, for example, in dispersing troops to avoid their all being taken out in a concentrated attack.
Bicyclists and other road users, on the other hand, don’t generally interact like prey and predators, or like armies in battle. I mean, motorists may sometimes be careless. A few may intentionally take risks with the safety of bicyclists and pedestrians, or be in denial about the hazards they pose. Motorists, however, generally aren’t intentionally out to kill and aren’t contemplating having us for dinner. What, then, is the mechanism of so-called “safety in numbers”? When might it exist, and when not?
First, there are different kinds of numbers.
- The general level of bicycling or walking in a population.
- Different locations in the same area that have different numbers of bicyclists/pedestrians/motorists, but all from the same general population.
- Different areas, with different populations and different rates of use.
- Numbers which increase on particular days, for example in nice weather.
- A population in the same area but changing over a span of years.
In an earlier post, I examined an Oakland, California study of pedestrian crashes at different intersections in the same community. The researchers’ text claims safety in numbers but the graphs show otherwise: the crash rate was moderately higher at intersections with more pedestrians. It was also higher at intersections with more motorists. It would take further analysis to determine how these two factors correlate with each other.
The well-known Jacobsen study of safety in numbers of bicyclists compared different communities at the same time. It also has been criticized (including in the Oakland study) for faulty math that shows a hyperbolic descending curve even if the input data are completely random.
In order to maximize safety, we need to know not only what happens, but also why. My own opinion is that there is generally an increase in safety over time as the number bicyclists and pedestrians increases. This occurs due to a number of different factors but also is impeded by others.
Some factors increasing safety:
- Longer experience, on average, of cyclists
- Cyclists’ better understanding of how to ride safely in a group
- Higher average age of cyclists
- Multiplicative effect of mentoring of cyclists by other cyclists (especially, children by parents)
- Change in attitude of motorists
- Presence of one cyclist directly increasing the safety of another by blocking traffic.
- Better facilities design, resulting from a more refined understanding of how to provide for bicyclists’ safety.
Some factors decreasing safety:
- Entry of new and inexperienced cyclists into the mix
- One cyclist’s concealing another from view when there many
- Sense of entitlement leading to scofflaw behavior
- False sense of security — “follow-the-leader” behavior when riding in a group
- Rush to build bicycle facilities, resulting in design compromises and inherent flaws
- Facilities that favor the least skillful, but are overprotective and frustrating for the more skillful, promoting scofflaw behavior
- Placing all eggs in the basket of “safety in numbers” and neglecting other approaches to increasing safety
There’s clearly much more research yet to be done in this field.