I am a cognitive scientist, a freelance writer and author (Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride), a musician (Parametric Monkey - stream on Spotify, Soundcloud and YouTube), a bookstore owner (Monkey Books - first edition mystery, science fiction, fantasy and more, listed on ABE books, Amazon and Biblio), and a retired house painter, children's theater actor & owner, and university professor. I'm also a regular contributor to the technology section at Forbes and I write a cycling blog called Tuned In To Cycling. You can follow me on twitter @TheInfoMonkey and contact me at murnane.kevin@gmail.com.

# The Safety in Numbers Effect

Does the chance of a cyclist being involved in a fatal accident increase as the number of cyclists on the road increases? The answer may surprise you. While the raw number of cycling fatalities does increase as the number of cyclists on the road increases, the chance that any one of those cyclists is killed is likely to decrease. This negative correlation between the number of cycling fatalities and the number of cyclists on the road is called the safety in numbers effect.

The graph above illustrates the safety in numbers effect by plotting the number of kilometers cycled per inhabitant along with the number of cycling fatalities for every billion kilometers traveled for various countries. The graph is from a research report published by the OECD (Organisation for Economic Co‑operation and Development) titled “Cycling Health and Safety.” The safety in numbers effect generally holds for pedestrians as well as cyclists.

The OECD report cautions against thinking that the negative correlation seen in the graph leads to the conclusion that increasing the number of cyclists causes a decrease in the likelihood of cycling fatalities. The report also mentions that there has not been very much research into the possible causes of the safety in numbers effect and goes on to suggest several factors that may be involved.

• Awareness: The more cyclists there are on the road, the more drivers will be aware of them. The more aware drivers are of cyclists, the less likely they are to hit them.
• Expectancy: The more cyclists there are on the road, the more drivers expect to see cyclists. The more drivers expect to see cyclists, the more likely they are to actually see them and avoid hitting them.
• Collective vigilance: The more cyclists there are on the road, the more likely it is that potentially dangerous or threatening situations will be noticed by at least one of them. Those who notice potential threats will communicate this information to the other cyclists who then have a greater chance to avoid the threat.
• Knowledgeable leaders: The more cyclists there are on the road, the greater the chance that at least one of them will be knowledgeable about route and traffic conditions. The knowledgeable cyclist may lead the others along safer routes.

It may also be the case that safety and the number of kilometers ridden are linked in a causal loop. The safer cycling is, the more people are likely to cycle, and the more people cycle, the more opportunity there is for awareness, expectancy, collective vigilance or knowledgeable leaders to have an effect in reducing fatal accidents.

The Hovenring in the Netherlands is the world’s first suspension bridge designed to allow cyclists and pedestrians to safely cross a busy highway intersection.

Another factor that almost certainly plays a role in both increasing the number of kilometers ridden and in reducing fatalities is the presence of a well-developed cycling infrastructure. The Netherlands, Denmark, and Germany, the three countries with the best fatalities to kilometers ridden ratios shown in the graph, also have exceptionally well developed cycling infrastructures.  The Netherlands and Denmark are especially notable in this regard. The United States, on the other hand, has generally lagged behind the rest of the developed world in building well-designed and well-maintained cycling infrastructure.  The better the infrastructure, the more people are likely to use it to cycle safely.

Dutch cyclists

Any or all of these factors – a strong social and cultural history of cycling, the presence of an excellent cycling infrastructure, driver awareness and expectation, cyclist vigilance and leadership – may have a role to play in explaining the safety in numbers effect. The negative correlation between fatalities and the number of kilometers ridden is simple and easy to see, the causal factors that produce this correlation are complex and difficult to tease apart.

# A Bike Share Map

Over 700 cities around the world have implemented bike sharing systems that allow people to make use of public bikes for short trips within the city.  The motivation is to reduce air pollution, noise and vehicular traffic congestion while providing people with the health benefits that come from daily exercise (which has been shown to decrease the costs of city-provided health services). The bikes can usually be used for free or for very low cost.

Oliver O’Brien, a researcher in the Geography Department of University College London has built a bike-share map that tracks the locations of bikes in the bike share systems of about 100 cities throughout the world. You can start with a global map and then click on the city of your choice to check out the more-or-less current state of the bike-sharing stations in the city. For example, here are the maps for Washington DC, New York, London, Paris, and Rio de Janeiro.

The circles on the city maps represent bike-share stations with the size of the circle indicating the number of bikes it can hold and the color indicating how full it is. For bike-share systems that allow it, the map updates about every two minutes. Some systems don’t permit updating this frequently and for this reason O’Brien advises against using the map to find out if there is a bike or an open space for a bike near you at any given moment. Unfortunately, the map does not tell you how often each city updates.

The bike-share map also has a tab that opens up a set of graphs showing how many docks are operating, how many bikes were in use and the imbalance in distribution of bikes over the system during the previous 24 hours.  In addition there is an animated version of the map that shows the docking station changes over the previous 48 hours which can be accessed from a tab at the bottom of the static map.

O’Brien has a blog that includes a post about the bike-share map in which he writes about things like where the data displayed in the map come from, and why some cities that have bike-share systems are not included on the map.