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Safety in Numbers
Overview
Safety in Numbers is the observation that the risk of an individual pedestrian or bicyclist being hit by a motor vehicle decreases as the number of pedestrians or bicyclists increases, respectively. This idea runs counter to what one might expect -- that the more pedestrians and bicyclists there are, the more collisions with motor vehicles will occur. Data show there is not a proportional relationship between these two variables. In fact, the safety in numbers relationship has been observed across a wide range of geographic study areas, from individual intersections to continents, [1] in the U.S., Europe, and Australia.
The Data
A widely cited 2003 paper by public health consultant Peter Jacobsen [1] examined injury rates, pedestrian and/or bicycle volume, and population over time in several different settings, with the following results:
- The likelihood of injury to a pedestrian or bicyclist in 68 California cities decreased as the percent of commuters walking or bicycling increased.
- A study of walking, bicycling, and moped use in 47 Danish towns found that walking was safer where there were more walkers and bicycling/moped use was safer where these modes were higher.
- The number of bicyclist fatalities per distance bicycled in 14 European countries decreased as the distance of bicycling per capita increased.
- In 8 European countries where data were available, the number of bicycling and pedestrian fatalities each decreased as per capita biking and walking trips increased, respectively.
- In Britain, bicycling varied up and down with different factors, such as the Arab Oil Embargo and new traffic speed laws, from 1950 to 1999. Whenever bicycling increased, per capita bicycling fatalities decreased, and the inverse was also true.
- In the Netherlands, where bicycling facilities and traffic law changes from 1980 to 1998 have greatly increased the amount of bicyclists and bicycle mileage, per capita bicycle fatalities have fallen equally dramatically.
Drivers More Cautious
What explains the safety in numbers for pedestrians and bicyclists? Traffic engineer and amatuer bicycling expert John Forester believes the relationship is a spurious correlation, with no proven cause.[3] But safety experts appear to disagree, and believe that motorists drive more cautiously when there are a larger number of walkers and bicylists in their environment. For example, Dr. Chris Rissel of Sydney University in Australia, stated in a 2008 interview, "It appears that motorists adjust their behavior in the presence of increasing numbers of people bicycling because they expect or experience more people cycling. Also, rising cycling rates mean motorists are more likely to be cyclists, and therefore be more conscious of, and sympathetic towards, cyclists."[4]
Jacobsen cites evidence from three studies that show drivers slow down when they see bicyclists and pedestrians, and speed up when they don't.[1] However, a better understanding of motorist behavior in this regard is needed. Nevertheless, it appears that any safe measures cities can take to make pedestrians and bicyclists more visible to motorists, and to encourage their numbers, will increase their average safety. That said, it is also true that walking and bicycling carry more risk of injury than driving in the U.S. [5] -- perhaps because the current traffic conditions are dangerous, and these dangers discourage higher volumes.
ALSO ON THE LIVABLE STREETS NETWORK
REFERENCES
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PICTURE REFERENCES
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[1] Courtesy of Pedestrian and Bicycle Information Center Image Library and Dan Burden.
[2] Courtesy of Pedestrian and Bicycle Information Center Image Library and Dan Burden.
