How do you Value a Life?

The current approach to road safety is failing us, by protecting private property over human lives. It’s time we flipped these priorities and started putting people first.


There’s been a lot of attention paid to road safety recently, and rightfully so. In many cities, people are getting fed up with the status quo and are feeling nervous to walk in their own neighbourhoods.

A great deal of effort goes into making streets safer, especially behind the scenes on the engineering side. Trained and experienced professionals are constantly at work assessing the safety of roadways, and measuring the benefits of safety improvements.

But what if the way we measure road safety is flawed? Safety assessments rely on fundamental assumptions about how we value safety, fatalities, and other forms of collisions. Understanding and discussing these assumptions is critical if we are to change the safety of our streets.

Quantifying Safety

Road safety analysis aims to understand the likelihood and severity of collisions, the latter of which are usually summarized into three types:

  • Property Damage Only (PDO): collisions where damage occurs to a vehicle or the built environment, where no one is injured, such as a car striking a sign post
  • Injury: collisions where someone is injured as a result of a road incident. Injury collisions are often broken out into different levels (ex. minor, severe, life-threatening)
  • Fatality: collisions where at least one person is killed, be it a pedestrian, cyclist, driver, or passenger

When engineers try to quantify the safety cost of a road, they assign “costs” to each of these collision types. If an investment in infrastructure can reduce collisions, the value of the prevented collisions is weighted against the cost of the infrastructure to determine if the investment is worthwhile.

This is where things get interesting, and where complex, subjective questions must be raised. What is the value of a human life? What is the societal cost of a fatality? Is it simply the cost to the medical system? Or the economic output that person could have produced if they had lived? Can we quantify the suffering caused to that person’s family?

While these questions are incredibly difficult to answer, even more interesting is that nobody seems to agree on the value of a life. Transport Canada pegs the cost of a transportation fatality at $16 million, while the Ontario Ministry of Transportation uses a value closer to a tenth of that.

Two-way protected bike lane in Ottawa, Canada

Imagine that building a protected bike lane could save one life over ten years, at a cost of $2 million. Is the cost of the lane worth the safety benefits? By how much? It’s important to understand the cost-benefit of a decision like this, and the benefit depends heavily on the value you assign to that saved life.

Isn’t it amazing then that this number, which is so difficult to quantify and agree on, is a fundamental ingredient in determining the investment we make in improving the safety of our roads?

What about PDOs?

Another important component to preventing road user deaths is the value we put on “property damage only” (“PDO”) collisions – not necessarily the value assigned, but the value relative to the value of a fatality collision.

To illustrate why, imagine that the average cost assigned to a PDO collision is $20,000, while the cost chosen for a fatality collision is $2 million. In this scenario, under a purely numbers-based approach to traffic safety, the safety benefit of preventing 100 PDO collisions is the same as preventing one fatality collision. In other words, preventing one hundred “fender-benders” is worth the same as saving a life.

Concrete barrier protecting a two-way bike lane in Brooklyn, New York

Let’s use an example of a cycle track running directly alongside a busy roadway. A designer proposes a concrete barrier to separate the bikeway from traffic, as a safety benefit to the cyclists using it. For motorists though, this concrete barrier creates a new hazard. Its position beside the roadway means that it will inevitably be struck many times by vehicles, with the vast majority of these incidents being property damage only (PDO) collisions.

An engineer then has to make an assessment on whether the concrete barrier delivers a net safety benefit to road users. She plugs in the numbers to a modelling software, and what does she find? Well, the result comes down to those key assumptions. If the relative cost of a PDO collision is high enough, the recommendation may be to not install the barrier, thereby saving property damage at the potential expense of human lives.

Who’s to judge where to draw the line? An advocate for vulnerable road users might protest that a human life is invaluable; that all fatalities should be prevented no matter the cost. But the reality is that funding for improving road safety is finite. The real question is, when we do invest dollars in safety, who (and what) are we trying to protect?

Vision Zero to the Rescue

How do you weigh the protection of private property against the preservation of human life? Vision Zero solves this dilemma, by requiring decision-makers to focus only on preventing collisions causing serious injuries and fatalities.

By rejigging the priorities, the equation changes entirely. Under a Vision Zero philosophy, engineers can justify adding elements of “friction” to roadways – that is, physical impediments and obstacles that force drivers to travel more slowly. This includes measures like placing trees right next to the curb of streets and narrowing lanes. In essence, drivers are forced to take the preservation of their private property (their cars) into their own hands by driving more carefully, providing immense safety benefit to all road users (including the drivers themselves).


As it stands today, our approach to road safety is failing us, by protecting private property over human lives. Vision Zero flips this equation on its head, putting the prevention of fatalities at the centre of focus. It’s time we demanded a more human-based approach to road safety.

A street designed with lots of “friction” to encourage very low traffic speeds in Groningen, Netherlands

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