A change in traffic accident (also called crash or collision) rates that results from a transportation project has an economic value.
Transportation planning decisions often affect crash risks. Benefit-cost analysis can help identify the most cost-effective projects and evaluate decisions that involve trade-offs between safety and other planning objectives, such as travel speed and vehicle costs.
Safety impact analysis requires information on how a project will affect crash frequency and severity. Most crashes are property damage only (PDO). Casualty crashes, in which somebody is injured, disabled or killed, are less frequent but much more costly to society. Crashes can impose a variety of market and non-market costs, include property damages, traffic delay, emergency response services, medical care and rehabilitation expenses, lost productivity, plus pain, suffering and grief.
Safety evaluation requires monetizing (measuring in dollar values) human life and safety. This can be controversial since some people fear that monetization implies that human life is a commodity, and from some perspectives human life has infinite value (most people would be unwilling to die for any amount of compensation). However, individuals and public agencies often make decisions that require trade-offs between incremental changes in safety and other benefits and costs. For example, motorists may need to decide whether to pay extra for an optional safety feature when purchasing a vehicle, and a transportation agency must decide whether to allow higher traffic speeds, or implement roadway design changes that affect crash rates. Applying monetized values helps make planning decisions that affect safety more consistent, and therefor more efficient and equitable.
Federal and state agencies have developed their own estimates for the economic value of preventing accidents, so the first step in an analysis is to choose which estimates are appropriate. Next, estimate the change in accident rates that the project is expected to create. Finally, use these data to estimate the economic value of the project's safety benefits.
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