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Safety in Numbers: More Riders Means Safer Streets

Bike to Work Day in San Francisco (photo courtesy of San Francisco Bike Coalition)

Although it sounds contradictory, the greater the number of people biking the safer the environment.

This concept of "Safety in Numbers" is not new. It was first observed in 1949 by Rueben Smeed, a British statistician and transport researcher. Using auto traffic data from 20 different countries, he developed Smeed's law which states that an increase in traffic would lead to a decrease in fatalities per vehicle. Since his death in 1976, the data set has been increased and validated in 62 countries.

The same inverse relationship has also been observed in biking and walking with data from 68 cities in California (Jacobsen). The researcher concluded a motorist is less likely to collide with a person walking and bicycling if more people walk or bicycle. How is this possible and how do different cities compare?

Researchers suspect that motorists adjust their behavior in the presence of people walking and bicycling. As a cyclist and a motorist this makes intuitive sense to me. ​In an environment, where you are constantly expecting bikers in the bike lane for instance, or pedestrians at the crosswalks it only seems natural that you pay more attention.

From personal experience, when I'm driving and see more bikers it increases my awareness of their presence and I drive more cautiously. How many of us have been in a car when a fellow passenger even says, "watch out for the biker".

Other factors that likely contribute to this phenomenon are bike infrastructure improvements such as signage, bike lanes, and sidewalks.. Also, a decrease in travel speeds may lead to the lower fatality rates. Drivers have a great field of vision at lower speeds and the impact of a crash is less lethal at lower speeds.

Bike Safety in Selected U.S. Cities

Using data from the National Highway Traffic Safety Administration (NHTSA) Fatality Analysis Reporting System (FARS) and American Community Survey, The Alliance for Biking & Walking has done some great analysis of cycling and fatality rates in large U.S. cities. 

In the graph below, orange dots represent bicyclist fatality rates -- i.e., the number of people who have died while biking as a portion of the number of people who bike to work. The grey line indicates the percentage of the population who bikes to work, and the green line shows correlation between the two. 

Chart showing inverse relationship between population biking to work and biking fatalities across 52 cities within the U.S.

The data clearly shows the inverse relationship between number of bike commuters and fatalities. Cities with the highest levels of bicycling generally have lower bicycle fatality rates including Portland, Minneapolis and Seattle. Chicago, where I bike to work, places in the top 1/3 of cities.

Tips for Safer Bike Commuting

It's important however to remember that there are people and individual stories behind each of these numbers. One traffic fatality is one too many. Worldwide there is a movement called Vision Zero guided by the principal that no traffic-related deaths are acceptable. And cities within the U.S. have started adopting it in their street designs and plans including New York, San Francisco, Seattle and Chicago among others.

And while riding is safer in an environment where are there are more riders, one cannot deny that there is danger involved. At an individual level, there are some important practices you can do to ride more safely including:

  1. Wear a helmet - one of the easiest and most effective things you can do is to wear a helmet; carrying the helmet on the handlebars or in your saddlebag does not count.

  2. Use lights - the data shows the majority of bike fatalities occur between 6-9 pm in the evening. It's imperative to make yourself visible. Here are some tips for riding safely at night.

  3. Ride defensively - yes, it must feel like a great sense of freedom to blow through a red light - but the truth is you are not invincible as a bike commuter. Rather, riding defensively is a much smarter approach. Behaviors like stopping at crossings, riding in the direction of traffic, slowing down when appropriate, and signaling when you are turning all contribute to a safer ride. ​

  4. Pay attention - as bikers in a car-dominated environment, we are vulnerable. It's critical to be mindful what's happening around you and in front of you - watch for opening doors, pedestrians crossing between parked cars, vehicles passing you and then slowing down to turn, potholes on the road. If it's too much to observe, then you are probably going too fast.

  5. Know the law - we could all use a little more street smarts. The Illinois Bicycle Safety quiz was developed as a way to educate both cyclists and motorist alike. Test your knowledge to see if you really know what the law says regarding cars and bikes.

Back to our man Smeed, He also postulated that 9 miles per hour is the minimum speed which drivers would tolerate in a congested environment. Below that, they would look to alternative modes of transportation. ​​Hmm, I wonder if he owned a bike?

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