Of all the urbanism specialists with tunnel vision, fire chiefs, fire marshals, and traffic engineers are probably the most dangerous. And by “dangerous,” I don’t just mean that they’re a threat to good urbanism; they also get people killed, which is exactly the opposite of what they are commissioned to do. A classic example of their silo thinking is playing out right now in Celebration, Florida, where the proposed measures of eliminating on-street parking spaces and eliminating street trees will almost certainly leave Celebration a less safe place than it is today.

More driving = more crashes and more deaths and injuries.

Let’s look at things from both a common-sense perspective and a data-driven perspective. Getting rid of street trees does some really bad things for safety: First, it eliminates the first line of defense for those who are walking or biking on the sidewalk (when the streets are too dangerous for biking). A car crashing into a tree at 35 miles per hour will deploy the airbags, but the driver and passengers will likely walk away with little more than bruises. But a car traveling 35 miles per hour that crashes into someone who is biking or walking will likely kill them. Higher speed = more deaths and injuries.

People adjust their driving according to the conditions around them. On a tree-lined street, people tend to drive slower because they don’t want to hit a tree if they lose control of their car and run off the road. Lower speed = fewer deaths and injuries.

There’s another problem with removing street trees: They make a huge difference between walking and driving in places that are hot in the summer (like Orlando). A canopy of street trees not only eliminates the strong radiant heat of the sun with its shade, but also cools you even further with the trees’ respiration, which has a similar effect to a cool mist. With a cooling canopy of street trees, most people walk well up into the 90s. With a hot sun beaming down, those same people rarely walk, even in the low 80s.

But there’s yet another problem: Humans get conditioned to everyday behavior, so when treeless streets condition them not to walk on moderately hot days, driving becomes their norm. And when you increase driving, you increase crashes and traffic deaths. There are even more reasons not to eliminate street trees, but that’s another story for another day, because it doesn’t involve safety.

On-street parking is equally essential to safety, and for even more reasons. As a matter of fact, on-street parking and street trees top the list of things cities should increase on streets if they’re interested in increasing the safety of their citizens. To be clear, the prime benefit of these two elements is getting people out of their cars because they prefer to walk to their daily needs. The two extremes are places where everyone drives (suburbia) and places where everyone walks (European towns and villages). Where everyone drives, there are huge numbers of deaths per year because of crashes. In most places where everyone walks, nobody has ever died due to running into someone else.