Iterating to Safety (Excerpt from Confessions of a Recovering Engineer)
The following is an excerpt from Chapter Five of Confessions of a Recovering Engineer: Transportation for a Strong Town, the latest book in the Strong Towns series. It has been slightly modified for this space. References to State Street in Springfield refer to a street in Springfield, Massachusetts, which we’ve written about extensively and is referenced throughout the book.
Confessions of a Recovering Engineer is available for preorder and will be released on September 8.
Image via Unsplash.
In the work that Urban3 has done modeling the financial productivity of different places, there is one correlation that stands out above all others. Wherever development patterns are most productive, wherever the highest value per acre is measured, those are the places where people will be found outside of a motor vehicle. Where humans are found in their habitat, those are the places building the greatest amount of community wealth. The more people that are consistently found, the more productive a place is likely to be. To borrow a phrase from ecology: People are the indicator species of success.
Since wealth is created by having humans naturally in their habitat, a prerequisite for building wealth is that a street be safe. The stroad-to-street conversion approach from Chapter Two is a good place to start: (1) slow traffic, (2) prioritize people over throughput, (3) build a productive place, and (4) embrace complexity. These are not steps to be done in series but four things to work on simultaneously.
As an example, many people—including myself, members of the Springfield city council, and the city’s engineering staff—have observed that people routinely struggle to cross State Street. Traffic moves too fast, and the gaps that people must cross while exposed to traffic are too great. The distance to signalized intersections is too great, and the time spent waiting and crossing is a higher threshold than people have shown they are willing to spend. This has been observed and well documented.
This is where we pull out the book Tactical Urbanism: Short-term Action for Long-term Change (Island Press, 2015) by Mike Lydon and Anthony Garcia and start trying things. On my own without collaboration and input from a Street Design Team, I am not absolutely positive where I would start, but my experience suggests that I would begin with paint and traffic cones at least 500 feet on each side of the entrance to the Springfield Central Library. In those places, I would start temporarily narrowing the lanes, changing the geometry of the street to figure out the best way to communicate to drivers that more caution, and slower speeds, are warranted.
In the last chapter, I explained the 85th percentile speed and how it relates to the comfort or tension people experience when driving. I wrote the following:
The only way to have meaningful reductions in speed, and a significant impact on the number of crashes, is through “geometric change.” The design of the street needs to prompt people to drive slower.
For streets, where we need complexity in order to build a productive place, traffic needs to flow at a neighborhood speed (15 mph or less is optimum) to make human habitat that is safe and productive. To achieve this on a street, the street design needs to shift drivers from the passive awareness of System 1 to the mental state of heightened engagement found in System 2.
Where traffic engineers have done a brilliant job recognizing the limits of human cognition and adjusting speed limits on roads to reflect the 85th percentile speed, they now need to apply the same insights to streets. The only difference is that, instead of using the 85th percentile speed to adjust the speed limit, on streets we need to use the measured speed to adjust the design.
Where drivers are traveling too fast, the geometry of the street needs to change, and keep changing, until a safe 85th percentile speed is achieved.
I would start with using paint and traffic cones to change the geometry of State Street, but I would keep iterating, trying new things, until I am able to measure the 85th percentile speed consistently at 15 miles per hour or less. At Strong Towns, we put this into a flow chart to draw a contrast between the way to use the 85th percentile speed on a road and a street.
The process will produce a design that works, albeit it a temporary installation. The Street Design Team can now get to work on ways to make this temporary design into something more permanent, understanding that the human habitat on State Street is going to continue to evolve, revealing more struggles that need to be responded to on a path to greater productivity.
It took Springfield, and cities across American, decades to build such expansive networks of dangerous and costly streets. It is going to take our cities time to unwind this mess. Tragedies such as the death of Destiny Gonzalez must be a catalyst for improving safety.
All cities need to use a Street Design Team to investigate, National Transportation Safety Board-style, every auto-related fatality in the community. Do not allow these incidents to be written off as merely driver error, but probe and document each contributing factor, including design. Respond to any design deficiencies rapidly using a low-cost Tactical Urbanism approach. Study and document driver and nondriver responses to identify changes that improve safety.
Take the lessons learned from investigations and tactical interventions and migrate them to other places within the community that have similar characteristics. Study tactical interventions in these new locations to corroborate or broaden findings. Then use ongoing maintenance as an opportunity to permanently implement the street designs that have been tested in your community and shown to lower speeds and improve safety.
Every city in North America, regardless of size or affluence, has an opportunity to make their streets safer while simultaneously reducing their public cost for infrastructure maintenance, enhancing their tax base to broadly build wealth, and improving the quality of life for people living within their community. That is the essence of a Strong Towns approach to streets. Our cities urgently need to get started.
Charles Marohn (known as “Chuck” to friends and colleagues) is the founder and president of Strong Towns and the bestselling author of “Escaping the Housing Trap: The Strong Towns Response to the Housing Crisis.” With decades of experience as a land use planner and civil engineer, Marohn is on a mission to help cities and towns become stronger and more prosperous. He spreads the Strong Towns message through in-person presentations, the Strong Towns Podcast, and his books and articles. In recognition of his efforts and impact, Planetizen named him one of the 15 Most Influential Urbanists of all time in 2017 and 2023.