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Safety in numbers

 

Safety in numbers

Safety in numbers is the hypothesis that, by being part of a large physical group or mass, an individual is less likely to be the victim of a mishap, accident, attack, or other bad event. Some related theories also argue (and can show statistically) that mass behaviour (by becoming more predictable and "known" to other people) can reduce accident risks, such as in traffic safety – in this case, the safety effect creates an actual reduction of danger, rather than just a redistribution over a larger group.

Contents

  • Description 1
  • In road traffic safety 2
    • Research 2.1
    • Criticism 2.2
    • Helmet debate 2.3
    • Examples of substantial increases in cycling associated with reduction in danger 2.4
      • Finland 2.4.1
      • London, UK 2.4.2
      • Berlin, Germany 2.4.3
      • Portland, Oregon, US 2.4.4
      • Copenhagen, Denmark 2.4.5
      • York, UK 2.4.6
      • Netherlands 2.4.7
      • Western Australia, Australia 2.4.8
      • Germany 2.4.9
      • New York, New York, US 2.4.10
  • See also 3
  • References 4

Description

Evidence often advanced for this position includes the flocking of birds and schooling of fish. In both of these instances, by being part of a large group, individuals face less risk of falling victim to predators than they would if traveling alone.

In road traffic safety

Safety in numbers is also used to describe the evidence that a motorist is less likely to collide with a pedestrian or cyclist as the numbers of pedestrians or bicyclists increase. This non-linear relationship was first shown at intersections.[1][2] A Public Health Consultant showed this non-linear relationship also occurs at in cities and countries using ecologic data from cities in California and Denmark, and European countries, and time-series data for the United Kingdom and the Netherlands. He termed this relationship "safety in numbers." [3]

Research

Substantial independent evidence shows that the number of pedestrians or bicyclists injured increases at a slower rate than would be expected based on their numbers. That is, the risk to the individual pedestrian or bicyclist decreases where there are more people walking or bicycling.[4] [5]

A 2002 study into whether pedestrian risk decreased with pedestrian flow, using 1983-86 data from signalized intersections in a town in Canada, found that in some circumstances the risk per pedestrian decreased with increased pedestrian flow.[6]

Criticism

A Cycling Transportation Engineer has disputed that conclusion, writing that the data used is insufficient to demonstrate that there is a cause-and-effect relationship.[7]

Another author has written that, while such data shows a degree of correlation, conclusions of causality may very well be based on a statistically spurious relationship. In other words, the relationship of an increase in bicycle use and a decrease in cyclist injuries may have no actual causal connection due to a certain third, unseen factor (referred to in statistics as a "confounding factor" or "lurking variable"). A spurious relationship gives an impression of a worthy link between two groups that is invalid when objectively examined.[8]

Helmet debate

Safety-in-numbers is important in the debate over the efficacy of bicycle helmets, because compulsory helmet laws have been shown to discourage bicycling. [9] Charles Komanoff has concluded that in "diluting the effect of 'safety in numbers,' compulsory helmet laws could have the perverse effect of increasing serious injury rates among those who continue to cycle." [10]

Examples of substantial increases in cycling associated with reduction in danger

Finland

After cycling was promoted in Finland, the number of trips increased by 72% and there was a 75% drop in cyclists deaths.[11]

London, UK

Between 2000 and 2008, the number of bicycle trips made in London, UK doubled. Over the same period, serious bicycle injuries declined by 12%.[12][13][14]

In the United Kingdom, Transport for London, the body responsible for the London Congestion Charge, stated in their April 2005 review of that scheme, that motor vehicle traffic had decreased by 16%, bicycle use had increased by 28% and cyclist injuries had decreased by 20% in the first year of operation of the scheme.[15]

In January 2008, a London newspaper reported that the number of cyclists in London being treated in hospitals for serious injuries had increased by 100% in six years. Over the same time, they report, the number of cyclists had increased by 84%.[16]

Berlin, Germany

Between 1975 and 2001, the total number of bicycle trips almost quadrupled. Between 1990 and 2007, the share of trips made by bicycle increased from 5% to 10%. Between 1992 and 2006, the number of serious bicycle injuries declined by 38%. [17][18]

Portland, Oregon, US

Between 1990 and 2000, the percentage of workers who commuted to work by bicycle rose from 1.1% to 1.8%. By 2008, the proportion has risen to 6.0%; while the number of workers increased by only 36% between 1990 and 2008, the number of workers commuting by bicycle increased 608%. Between 1992 and 2008, the number of bicyclists crossing four bridges into downtown was measured to have increased 369% between 1992 and 2008.

During that same period, the number of reported crashes increased by only 14%. [19][20][21]

Copenhagen, Denmark

Between 1995 and 2006, cycling increased by 44% and the percent of people cycling to work increased from 31% to 36%. During the same period, the number of cyclists killed or seriously injured fell by 60% [22]

York, UK

Comparing the periods 1991-93 and 1996–98, the share of trips made by bicycle rose from 15% to 18%. The number of bicyclists killed and seriously injured fell by 59%. [23]

Netherlands

Between 1980 and 2005, cycling increased by 45%, and cyclist fatalities decreased by 58%. [24]

Western Australia, Australia

During 7 years of the 1980s, cycling in Western Australia increased by 82% and admissions to hospital of cyclists declined by 5%. [25]

Germany

Between 1975 and 1998, the percent of trips made by bicycle rose from 8% to 12%, and cyclist fatalities fell by 66%. [26]

New York, New York, US

During the period 1999-2007, the amount of cycling increased by 98%, and the absolute number of cyclists killed or seriously injured decreased by 29%. [27][28][29]

See also

References

  1. ^ Brüde, U., Larsson, J. (1993). "Models for predicting accidents at junctions where pedestrians and cyclists are involved. How well do they fit?". Accident Analysis and Prevention 25 (5): 499–509.  
  2. ^ Leden, L., Gårder, P., Pulkkinen, U. (2000). "An expert judgment model applied to estimating the safety effect of a bicycle facility". Accident Analysis and Prevention 32 (4): 589–599.  
  3. ^ Jacobsen, P. L. (2003). "Safety in numbers: more walkers and bicyclists, safer walking and bicycling". Injury Prevention 9 (3): 205–209.  
  4. ^ Elvik, R. (2009). "The non-linearity of risk and the promotion of environmentally sustainable transport". Accident Analysis and Prevention 41 (4): 849–855.  
  5. ^
    • Geyer, J. Raford, N., Pham, T., Ragland, D. (2006). "Safety in Numbers: Data from Oakland, California". Transportation Research Record 1982: 150–154.  
    • Miranda-Moreno, L., Strauss, J., Morency, P., (2011). "Disaggregate Exposure Measures and Injury Frequency Models of Cyclist Safety at Signalized Intersections". Transportation Research Record 2236 (2236): 74–82.  
    • Raford, N., Ragland, D. (2004). "Space Syntax: Innovative Pedestrian Volume Modeling Tool for Pedestrian Safety". Transportation Research Record 1978: 66–74.  
    • Schneider, R., Chagas Diogenes, M., Arnold, L., Attaset, V., Griswold, J., Ragland, D. (2010). "Association Between Roadway Intersection Characteristics and Pedestrian Crash Risk in Alameda County, California". Transportation Research Record 2198: 41–51.  
    • Harwood, D.W., Torbic, D.J., Gilmore, D.K., Bokenkroger, C.D., Dunn, J.M., Zegeer, C.V., Srinivasan, R., Carter, D., Raborn, C., Lyon, C., Persaud, B. (2008). "Pedestrian Safety Prediction Methodology" (PDF). NCHRP Web-only Document 129: Phase III. Transportation Research Board, Washington, DC. 
    • Jonsson, T. (2005). "Pedestrian Safety Prediction Methodology". Predictive models for accidents on urban links. A focus on vulnerable road users. Ph.D. Dissertation. Bulletin 226. Lund Institute of Technology, Department of Technology and Society, Traffic Engineering, Lund. The validation indicated that exponents were 0.5 for both the flows of pedestrians and motor vehicles in models for accidents involving vulnerable road users, and 1.0 for the motor vehicle flow exponent in the models for motor vehicle accidents. For bicyclist accidents the correct exponent for bicyclist flows is likely to be somewhat lower than 0.5, close to 0.35. 
    • Lyon, C., Persaud, B.N. (2002). "Pedestrian collision prediction models for urban intersections". Transportation Research Record 1818: 102–107.  
    • Robinson, D.L. (2005). "Safety in numbers in Australia: more walkers and bicyclists, safer walking and cycling". Health Promotion Journal of Australia 16 (1): 47–51.  
    • Jensen, S. U., Andersen, T., Hansen, W., Kjærgaard, E., Krag, T., Larsen, J.E., Lund, B.L. Thost, P. (2000). "Collection of Cycle Concepts" (PDF). A publication of Road Directorate, Denmark: 15. 
    • Jensen, S.U. (1998). "DUMAS – Safety of Pedestrians and Two-wheelers". A publication of Road Directorate, Denmark: Note 51. when pedestrian and cycle traffic increases, the casualty rate per kilometre decreases. 
    • Elvik, R. (2009). "The non-linearity of risk and the promotion of environmentally sustainable transport". Accident Analysis and Prevention 41 (4): 849–855.  
    • Daniels, S., Brijs, T., Nuyts, E., Wets, G. (2010). "Explaining variation in safety performance of roundabouts". Accident Analysis and Prevention 42 (2): 393–402.  
    • Vandenbulcke, G., Thomas, I., de Geus, B., Degraeuwe, B., Torfs, R., Meeusen, R., Panis, L.I. (2009). "Mapping bicycle use and the risk of accidents for commuters who cycle to work in Belgium". Transport Policy 16 (2): 77–87.  
    • Ekman L. (1996). "On the treatment of flow in traffic safety analysis — a non-parametric approach applied on vulnerable road users". Lund, Sweden: Institutionen för Trafikteknik, Lunds Tekniska Högskola. Bulletin 136. the conflict rate for bicyclists is twice as large at locations with low bicycle flow compared to locations with higher flow 
    • Turner, S.A., Roozenburg, A.P., Francis, T. (2006). "Predicting accident rates for cyclists and pedestrians" (PDF). Land Transport New Zealand. Research. Report 289. A 'safety in numbers' effect is observed for cycle accidents at traffic signals, roundabouts and mid-block sites. An increase in cycle numbers will not therefore necessarily increase the number of accidents substantially. A 'safety in numbers' effect is also observed for pedestrian accidents at traffic signals and mid-block sites. Insufficient data exists to conclude whether a 'safety in numbers' effect occurs at roundabouts 
    • Turner, S.A., Binder, S., Roozenburg, A.P. (2009). "Cycle Safety: Reducing the Crash Risk" (PDF). Land Transport New Zealand. Research. Report 389. As shown in figure 2.20, an increase in the proportion of cyclists to the overall traffic volume causes an increase in expected crashes at mid-block locations, but the crash rate increases at a decreasing rate. That is to say, the crash rate per cyclist goes down as the cycle volume increases. 
    • Knowles, J., Adams, S., Cuerden, R., Savill, T. Reid, S., Tight, M. (2009). "Collisions involving pedal cyclists on Britain's roads: establishing the causes". Transport Research Laboratory Published Project. Report. PPR445. The research assessed as part of this study is strongly suggestive that a safety in numbers effect exists. 
    • Noland, R.B., Quddus, M.A., Ochieng, W.Y. (2008). "The effect of the London congestion charge on road casualties: an intervention analysis" (PDF).  
    • Ministerie van Verkeer en Waterstaat (2009). "Cycling in the Netherlands" (PDF). p. 14. 
    • Pucher J., Dijkstra L. (2000). "Making walking and cycling safer: lessons from Europe" (PDF). Transportation Quarterly 54 (3): 25–50. 
    • Turner S.A., Wood, G.R., Luo, Q., Singh, R., Allatt, T. J., Affiliation: Civil and Natural Resources Engineering, University of Canterbury, New Zealand; Macquarie University, NSW, Australia; Beca Infrastructure Ltd, New Zealand. (2010). "Crash prediction models and the factors that influence cycle safety". Australas Coll Road Saf 21 (3): 26–36. The key finding is that as cycle volumes increase, the risk per individual cyclist reduces - the 'safety in numbers' effect. 
    • Tin Tin, S., Woodward, A., Thornley, S., Ameratunga, S. (2011). "Regional variations in pedal cyclist injuries in New Zealand: safety in numbers or risk in scarcity?". Australian and New Zealand Journal of Public Health 35 (4): 357–363.  
    • Daniels, S., Brijs, T., Nuyts, E., Wets, G (2011). "Extended prediction models for crashes at roundabouts". Safety Science 49 (2): 198–207.  
    • de Geus B, Vandenbulcke G, Int Panis L, Thomas I, Degraeuwe B, Cumps E, Aertsens J, Torfs R, Meeusen R. (2012). "A prospective cohort study on minor accidents involving commuter cyclists in Belgium". Accident Analysis & Prevention 45 (2): 683–693.  
    • Nordback K, Marshall W, Janson B (2014). "Bicyclist safety performance functions for a U.S. city". Accident Analysis & Prevention 65: 114–122.  
  6. ^ Leden, L. (2002). "Pedestrian risk decrease with pedestrian flow. A case study based on data from signalized intersections in Hamilton, Ontario". Accident Analysis and Prevention 34 (4): 457–464.  
  7. ^ Forester, John. "Does Increasing the Number of Cyclists Reduce the Accident Rate?". Review of Safety in Numbers. Retrieved 2006. 
  8. ^ Burns, William C. (1997). "Spurious Correlations". Retrieved 2008. 
  9. ^ Robinson D.L (1996). "Head injuries and bicycle helmet laws". Accident Analysis and Prevention 28 (4): 463–75.  
  10. ^ Komanoff, C. (2001). "Safety in numbers? A new dimension to the bicycle helmet controversy [Letter]". Injury Prevention 7 (4): 343.  
  11. ^ Saari R. (2005). "Cycling policy in Finland and relevance of CBA for the policy. In: CBA of Cycling. Copenhagen, Nordic Council of Ministers, 556". Retrieved 2007. 
  12. ^ "The London Cycling Action Plan. Transport for London, London, UK" (PDF). Transport for London. 2004. 
  13. ^ "Cycling in London: Final report. Transport for London, London" (PDF). Transport for London. 2008. 
  14. ^ "Central London congestion charging: Impacts monitoring, Sixth Annual Report. Transport for London, London". Transport for London. 2008. 
  15. ^ Transport for London (April 2005). "Congestion Charging: Third Annual Monitoring Report." (PDF). 
  16. ^ Nicholas Cecil (2008-01-28). "Number of cyclists treated for serious injuries doubles". Evening Standard. Retrieved 2008-01-30. 
  17. ^ Senatsverwaltung fuer Stadtentwicklung. Office of Urban Development, Berlin, Germany (2003). "Focus on bicycling". 
  18. ^ Pucher, J. and Buehler, R. (2007). "At the frontiers of cycling: Policy innovations in the Netherlands, Denmark, and Germany". World Transp. Policy Pract. 13 (3): 8–57. 
  19. ^ US Census Bureau (2009). "American FactFinder". 
  20. ^ City of Portland, Portland Bureau of Transportation (2008). "Portland bicycle counts 2008". 
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  22. ^ City of Copenhagen Traffic Department (2007). "Copenhagen, city of cyclists: bicycle account 2006" (PDF). 
  23. ^ Harrison, J. (2001). "Planning for more cycling: The York experience bucks the trend". World Transport Policy & Practice 7 (4). 
  24. ^ Ministerie van Verkeer en Waterstaat (2007). "Cycling in the Netherlands". 
  25. ^ Robinson, D. (2005). "Safety in numbers in Australia: more walkers and bicyclists, safer walking and bicycling" (PDF). Health Promotion Journal of Australia 16 (1): 47–51.  
  26. ^ Pucher, J. and Dijkstra, L. (2000). "Making walking and cycling safer: lessons from Europe" (PDF). Transportation Quarterly 54 (3): 25–50. 
  27. ^ NYC DOT (2008). "Safe Streets NYC: Traffic Safety Improvements in New York City". 
  28. ^ A Joint Report from the New York City Departments of Health and Mental Hygiene, Parks and Recreation, Transportation, and the New York City Police Department (2005). "Bicyclist Fatalities and Serious Injuries in New York City 1996-2005". 
  29. ^ "New York City Commuter cyclist indicator" (PDF). 
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