Rethinking Transportation Safety

Todd Litman's picture

A paradigm shift is changing the way we think about transportation safety. In the past, traffic safety experts evaluated risk using distance-based units (traffic crashes and casualties per 100 million vehicle-miles or billion vehicle-kilometers), which ignores increases in vehicle traffic as a risk factor, and mobility management as a safety strategy. Yet, we now have overwhelming evidence that the amount people drive has a major impact on their chance of being injured or killed in a traffic accident. Here is a small portion of the evidence:

·     Urban Sprawl As A Risk Factor In Motor Vehicle Occupant And Pedestrian Fatalities (Ewing, Schieber and Zegeer, 2003, American Journal of Public Health, Vol. 93, No. 9, pp. 1541-1545). This study found that residents of the most sprawled U.S. counties have about four times the average traffic fatality rate as residents of the least sprawled counties, as illustrated below.

Sprawl increases traffic fatality rates

Residents of the smartest growth counties have about a quarter the per capita traffic fatality rates as residents of the most sprawled counties. 

·         Is The U.S. On The Path To The Lowest Motor Vehicle Fatalities In Decades? (Michael Sivak, 2008, Report UMTRI-2008-39, University of Michigan Transportation Research Institute). This study found that high fuel prices caused vehicle travel reductions that resulted in proportionately larger reductions in traffic fatalities (i.e., a 10% reduction in mileage causes a 15-20% reduction in traffic fatalities).

·       Safe Travels: Evaluating Mobility Management Traffic Safety Impacts (Todd Litman and Steven Fitzroy, 2006, Victoria Transport Policy Institute). This study indicates that per capita traffic fatalities decline as public transit and nonmotorized travel activity increase, as illustrated below.

Per capita traffic fatalities decline as per capita transit travel increases.

Per capita traffic fatalities tends to decline with increased transit ridership. These values include deaths to transit passengers, automobile passengers, and pedestrians. ("Large Rail" refers to cities with large, well established rail transit systems).

·         Safety In Numbers: More Walkers and Bicyclists, Safer Walking and Bicycling (Peter L. Jacobsen, 2003, Injury Prevention, Vol. 9, 2003, pp. 205-209). This and several more recent studies show that total crashes decline as walking and cycling increase in a community.  

Truly optimal traffic safety policies require changing the way we think about, evaluate and implement traffic safety. Transportation policies that stimulate increased driving are likely to increase traffic risk, while mobility management strategies that reduce total vehicle travel and encourage shifts to alternative modes are likely to increase traffic safety.

The new paradigm greatly expands the range of traffic safety strategies, including improvements to alternative modes, pricing reforms, and smart growth land use policies. It also requires considering co-benefits, since mobility management strategies can also help solve other problems, such as traffic and parking congestion, pollution emissions, excessive consumer costs, inadequate mobility for non-drivers, and inadequate public fitness and health.

Mobility management requires new approaches and relationships. For example, traffic safety professionals will need to become involved in transport planning and investment decisions, transport pricing policies, and land use planning practices, in order to create truly safe and healthy communities. This will require partnerships with local governments and school districts (to increase the feasibility of walking to local destinations, such as schools), state and federal policy makers (to support transportation pricing reforms such as increased fuel taxes and distance-based pricing), developers and real estate agents (to build and sell more walkable, less automobile dependent neighbourhoods), and the insurance industry (to create and promote pay-as-you-drive vehicle insurance), to name a few.

Paradigm changes are initially difficult. We are now at the stage in which many experts are still unfamiliar with the issues and dismiss evidence that justifies reforms. For example, many traffic safety professionals still insist on using distance-based units to measure risk, which makes existing traffic safety strategies look successful. They continue to ignore the safety risks of sprawl and the safety benefits of traffic reduction policies. They refuse to consider mobility management strategies when developing traffic safety programs, and undervalue these programs by ignoring co-benefits such as congestion reductions and consumer cost savings.

But this will change. Soon enough, the new paradigm will become ingrained into the traffic safety culture. These same traffic safety experts who currently ignore mobility management will soon embrace it and claim that they invented these ideas in the first place.

 Information Resources

Peggy Edwards and Agis D. Tsouros (2008), A Healthy City Is An Active City: A Physical Activity Planning Guide, World Health Organization Europe (; at

Lawrence Frank, Sarah Kavage and Todd Litman (2006), Promoting Public Health Through Smart Growth: Building Healthier Communities Through Transportation And Land Use Policies, Smart Growth BC (; at

Peter L. Jacobsen (2003), "Safety In Numbers: More Walkers and Bicyclists, Safer Walking and Bicycling." Injury Prevention (, Vol. 9, 2003, pp. 205-209; at

Todd Litman (2004), If Health Matters: Integrating Public Health Objectives into Transportation Decision-Making, Victoria Transport Policy Institute (; at; previously published as, "Integrating Public Health Objectives in Transportation Decision-Making," American Journal of Health Promotion, Vol. 18, No. 1 (, Sept./Oct. 2003, pp. 103-108; at 

Todd Litman and Steven Fitzroy (2006), Safe Travels: Evaluating Mobility Management Traffic Safety Benefits, Victoria Transport Policy Institute (; at

William H. Lucy (2003), "Mortality Risk Associated With Leaving Home:  Recognizing the Relevance of the Built Environment," American Journal of Public Health, Vol 93, No. 9, September 2003, pp. 1564-1569; at

WHO (2004), World Report on Road Traffic Injury Prevention, World Health Organization and World Bank (; at


Todd Litman is the executive director of the Victoria Transport Policy Institute.


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