January 8, 2024 BY Tiffany Smithin News

Thinking & Acting Differently for Vision Zero: Applying the Health Impact Pyramid to Roadway Safety

Imagine if we depended on each person in the country to figure out their own plan to get clean water to their individual household, rather than investing in a shared filtration and sanitation system to provide safe, clean drinking water to the entire community. Fortunately, wise people have figured this out, and we all benefit.

But when it comes to staying safe moving about our communities – walking to school, driving to work, biking to meet friends in the park – we simply have not built a strong enough community-wide safety system for all. While there are safety rules and systems in place, it is too often the case that we lean on individuals to “do the right thing” in order to stay safe, rather than baking safety fully into the transportation system we all use every day.

As we grapple with how to address the mounting roadway safety crisis in this country – more than 42,000 preventable traffic deaths in 2022 – we can learn lessons from the public health sector about how to invest in more effective system-wide safety interventions rather than over-relying on individual-level actions. 

Our recent webinar, in collaboration with the Institute for Transportation Engineers (ITE), explored what a public health approach to roadway safety means and highlighted key elements of a new research paper highlighting timely opportunities for transportation professionals to apply health principles to their safety efforts. Joined by panelists David Ederer from the Centers for Disease Control and Prevention (CDC), Meghan Mitman of Fehr & Peers, and Tiffany Smith from the Vision Zero Network, the webinar discussion explored both strategies and frameworks to help practitioners implement a more effective, public health-inspired Safe System approach. 

Following are some of our key takeaways: 

Applying the Health Impact Pyramid to Roadway Safety

While many Vision Zero efforts underscore the importance of collaborating with your local public health department in order to better understand the health impacts of transportation decisions, pinpoint key injury risks, and contextualize how roadway safety disparities show up in communities, we can and should go further with integrating public health frameworks more fundamentally in road safety work. 

According to the work by Ederer and his co-authors,Rachael Thompson Panik, Nisha Botchwey, & Kari Watkins, there has been much research on how transportation influences health outcomes, but relatively little guidance on how to apply public health concepts to roadway safety work.

Public health practitioners use the Health Impact Pyramid (HIP) to discern which strategies require the most individual effort with the least population impact, (see those at the top of the pyramid, below), and which require the least individual effort with the most population impact (bottom). The more individual effort required for an intervention means little to no impact on a  population level and vice versa. 

Interventions that address socioeconomic factors have the greatest potential for impact on health because they reach entire populations of people at once and require significantly less individual effort to be effective.

Developed in 2010 by Thomas Frieden of the Centers for Disease Control and Prevention, the Health Impact Pyramid is a framework that visually depicts the potential impact of different types of public health interventions and can be applied to the Safe System approach that underlies Vision Zero.

Does this sound familiar? If so, it’s because it is! These health impact principles are also reflected in the principles of the Safe System approach, which underlies Vision Zero. These emphasize upstream strategies, such as redesigning roadways, adding life saving technology in vehicles, and lowering speed limits, each of which have a high, positive population-level impact. David Ederer & his co-authors adapted the Health Impact Pyramid framework into the Safe System Pyramid for roadway safety practitioners (below). It shows how different interventions in the Safe System pyramid (below) require more individual effort and which have a larger population impact

The Safe System Pyramid (referenced above) was adapted from the Health Impact Pyramid to more fully address roadway safety needs.

For example, an individual-level strategy is encouraging people to drive a safe speed via education campaigns (billboards, radio ads) and the threat of getting speeding tickets. These have some, but not widespread, deep and lasting impacts. Meanwhile, a population-level strategy would be road designers physically separating people driving from people walking and biking wherever possible with fully separated, Complete Streets; another is slowing speeds whenever possible with traffic calming features on the road and lowering speed limits, so that if/when a crash happens, it is less severe. These population-level strategies are what we consider an “upstream” focus in Vision Zero, having far greater, more lasting safety impacts.

Working Beyond the Tip of the Iceberg

Part of the reason we are not making progress in the U.S. in improving roadway safety and trailing behind so many other nations, is that we are only working at the tip of the iceberg. Instead of digging into and addressing the deeper, root causes of what make our roadways unsafe, we have been relying too much on surface-level solutions, which do not adequately address the fundamental, systemic problems. 

Too often, people think that we can simply educate and enforce our way out of the current situation by encouraging people to “do the right thing” on our roadways. But the reality is that we are moving about in a very imperfect transportation system that often enables – or even encourages – dangerous behavior. We know that people are more likely to behave safely when they are offered safe mobility options and move about in safe environments. 

So, it’s time to focus on systemic level solutions, such as redesigning the built environment, lowering speed limits and setting policies to bolster these changes to make safe driving behavior the easiest choice.

Some ways to work beyond the tip of the iceberg are highlighted below:

Addressing Socioeconomic Factors: While transportation is often thought of as a means to an end, decisions related to our transportation systems and the crashes that occur within these systems intersect with many consequential aspects of our lives, including but not limited to our access to employment, education and medical care, making it a key social determinant of health. Essentially, where we live, the jobs we have, where we work, where we go to school, and other factors not only affect our health but impact how we move through our community.

Rarely, however, is access to critical destinations like healthcare, education, and employment, included in roadway safety planning, which directly contrasts with public health principles that recognize how strongly income levels impact how we travel from point A to B. Some communities, particularly people in low-income neighborhoods and communities of color, are disproportionately exposed to dangerously built environments with poorly designed, high traffic, high-speed roads and a lack of good sidewalks and bikeways. Traditional PR campaigns, which are often used as a roadway safety strategy, remind people to use crosswalks, sidewalks, and to “be safe” while walking – but these campaigns rest on the assumption that there are safe walking choices and infrastructure to begin with, which is often not the case, especially in traditionally underserved communities.

Recognizing and rectifying these transportation disparities is an opportunity to work at the important base of the Safe System pyramid to have more positive and lasting population impacts and to institutionalize health equity in this work. Learn more about how to institutionalize health equity in your roadway safety work in our new resource, Prioritizing Health Equity in Vision Zero Planning.

Vision Zero Network’s framework for health equity in Vision Zero, taken from our resource, Prioritizing Health Equity in Vision Zero Planning

Focusing on the Built Environment: Too often, racialized enforcement, including discriminatory traffic stops and unjust fines and fees, are used in the name of “safe streets.” An overemphasis on enforcement overlooks the fact that today’s transportation system is not generally designed to reward or encourage safe behavior

When put into a public health context, scaling up enforcement without focusing on the built environment is similar to only treating “sick” individuals once they fall ill without ever working upstream to prevent transmission of that illness among an entire population. An example to curb dangerous speeding is addressing the built environment features that enable (or even encourage) speeding to occur in the first place, such as wide travel lanes and high speed limits. Doing this will be more effective at lowering speeds overall, offering a significant population level impact, compared to the traditional approach of focusing primarily on targeting individual drivers and changing their behavior with education and enforcement campaigns.

The Safe System Pyramid, referenced above, highlights the lower levels of the pyramid as having the highest population level impact

Moreover, addressing the built environment is similar to the Safe System elements of Safe Streets & Safe Speeds, which includes designing transportation systems in ways that separate users in space, such as bikeways and sidewalks for people walking. But also in ways that separate users in time, such as adjusting corridor signal timing or implementing leading pedestrian intervals, which allow pedestrians to cross intersections before cars, reducing potential conflict points between cars and other road users (learn more about how this works from ITE).

By separating users in time and space we can also directly manage both the speed and impact of that speed on the human body, or the transfer of energy between cars and people walking and biking, if and when a crash occurs. This energy transfer is the most important E we should be prioritizing. 

Focusing on Energy (the most important “E”)

The impact of energy (risk of injury and fatality) increases as speeds increase. source Federal Highway Administration (FHWA)

Historically, roadway safety has primarily focused on meeting what’s called the desired Level of Service (LOS). But as Meghan Mitman, from Fehr & Peers, highlighted in the webinar, “What if we thought of level of safety, instead of level of service?” 

But how do you measure safety? One important way is how we manage the transfer of kinetic energy on the roadways. This means wherever possible prioritizing interventions that keep impacts on the human body at tolerable levels: prioritizing the management of energy transfer in areas where people walking and biking are mixing with drivers, and designing streets for desired, safe speeds, instead of predominant speeds. Learn more about Energy - the only E that matters in this post from  Michael King, an architect turned urban planner focused on managing energy in the built environment.

In practice, this means setting lower speed limits in areas where we know people are walking and biking, and either retrofitting these roadways with roundabouts or speed humps, or enacting Complete Streets policies to create dedicated space for people walking and biking where they are mixing with drivers, so that roadway designs truly complement their lowered speed limits. It is, in essence, choosing safety OVER speed in design and policies. 

What acting quicker and more efficiently mean in practice, highlighted by Meghan Mitman from Fehr & Peers

Focusing on Change Management

But what do institutionalizing these ideas look like in action? Meghan Mitman highlighted three ways to move beyond the tip of the iceberg and pivot to a more comprehensive and public health based approach to roadway safety work.

  • Doing more & acting more quickly and efficiently by moving away from and rebalancing the Es. An equivalency of all the conventional Es (education, engineering, enforcement, etc.) misses the point of the pyramid, where engineering and the built environment have the biggest positive population impacts for safety. If we know that separating users in time and space has a significant impact on energy transfer between cars and other road users, then we should be scaling up these infrastructure elements in areas where we know people are walking and biking, rather than waiting for crashes to  happen before taking action. This means scaling up treatments like signal retiming for 25mph, adding speed humps and leading pedestrian intervals, which are simple and low cost to implement, but also effective at reducing failure to yield, speeding, and turning-related crashes. This also means obtaining more funding for quick builds and pilot (or demonstration) projects, which can be funded through the Safe Streets and Roads for All grant program and other sources. Learn more
  • Looking upstream to broader planning & policy efforts. Safety is not just a transportation issue, but a cross-cutting one. So collaboration is critical to infuse safety into all things that interact with transportation, such as coordinating with land-use and housing policies and projects. It also means reforming internal processes that are inconsistent with what we know to be both effective and has far reaching impacts. For instance, instead of measuring Level of Service (L.O.S.), specific to traditional transportation analyses and prioritizing car flow, we could switch to measure vehicle miles traveled, which reflects environmental and health impacts. California has already made this change by law to promote multimodal transportation and more diverse land uses.
  • Getting out of our own way by learning from epidemiologists and adopting the principles of injury prevention. And then translating and communicating what we know to be effective across different audiences in forming the “magic triangle” of agencies, advocates, and electeds. These are the key players who can make the systemic changes and policies that support safety. Advocates are especially important, as they can raise awareness about the necessity for these changes, provide additional context on safety needs, and can help maintain both momentum and longevity of safety-centered infrastructure.

The Magic Triangle of making change, highlighted by Meghan Mitman from Fehr & Peers

We know we can do better because we HAVE the tools to do better. And we are eager to learn from and uplift successful models from the public health world to inform our roadway safety efforts. Let’s find ways - both big and small - to more closely align Vision Zero planning and ongoing work with public health principles and the Safe System pyramid.

Read more about the Safe System Pyramid and how to Prioritize Health Equity in Vision Zero Planning. Thank you to ITE for inviting us to co-host this webinar and for advancing the conversation & discussion around the role of public health & safe system approach principles in meaningful roadway safety work. 

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