When people talk about how cities can relieve congestion, it’s essential to think about our physical spaces in ways people aren’t really accustomed to thinking about them. We get used to the world around us, and things that are problems seem normal and acceptable. Cars are so ubiquitous, their presence everywhere so natural, that we seldom question just how much space they take up and how this contributes to congestion.

I’d like to explore this question more to show the problem clearly.

I recently finished a wonderful book called Killed By a Traffic Engineer, written by traffic engineer Wes Marshall, about how the underlying assumptions engineers make are the root causes of many safety problems we have on the roads and, therefore, in our cities.

The book is made up of 88 small chapters, usually four or five pages. One section I found devastating was about “clear zones,” the phrase given to the space on the road outside the laneways that needs to be cleared of any physical objects for “safety” reasons. The specifications are strict, even if the underlying assumptions are dubious.

A 1963 roadside design guidebook called the Automotive Safety Foundation (ASF) said that since so many accidents involve vehicles leaving their travel lanes, accounting for 30-35% of fatalities at the time, it was essential for roads to have a certain amount of free space outside the lanes for errant vehicles, so that a car leaving its lanes wouldn’t crash into anything.

On a certain level, this makes sense. If there’s nothing there, there’s nothing to crash into! Anyone imagining a car swerving out of its lane understands that it’s safer for there to be no physical object outside.

But the ASF determined that 25% of crashes involved trees, so what did they do? They cut down all the trees beside roads. This, even though the ASF guidebook recognized that no research proved that proximity to a fixed object increased the likelihood of a crash. In other words, in the event of a crash, it’s safer to have a clear zone than not to, but no research confirms that clear zones make a crash less likely. If anything, there’s evidence they make crashes more likely. Nonetheless, clear zones became the norm moving forward. Often, big ones.

In 1967, 30 feet of clearance space on either side of the road was considered appropriate. The engineers had a different set of fatality reduction at every 5-foot interval, so a 5-foot clear zone led to a 13% reduction in fatalities, a 10-foot 25%, 20-foot 44%.

On rural highways, this makes sense. The problem begins when cities started turning urban streets into rural highways. Do you want a city with trees in it? Because you can’t have tree-less arterial roads and an abundance of trees. How do you create a 30-foot buffer on either side of the road in a world with thousands of pedestrians and cyclists? A city without trees and human beings is sad indeed.

On a fundamental level, there’s an error in the assumptions going on here. Giving drivers an impossibly wide, undisturbed road may make them drive faster than they would if laneways were narrower, increasing the danger. That’s why the clear zones might increase the danger. If stats show there are fewer pedestrian collissions on such streets, it may be because fewer people walk around highway-like streets in cities.

Wes Marshall points out that urban roadways had a lower fatality rare than rural ones according to Traffic Quarterly data from 1959 and 1963. Crash injury rates were also double in rural environments than urban ones.

It turns out that the “hazards” alongside the road may also encourage safer driving habits. People behind the wheel tend to slow down when less room is available to them, and this leads to real increased safety. Empirically, there’s no proof that “clear zones” improve road safety.

There’s nothing innately safer about removing all potential obstacles. If cities were to make walking on city streets illegal–if Toronto outlawed walking on the sidewalks and roads–then you’d have stats showing there were no pedestrian deaths. Does this mean the city is safer for pedestrians? Causality is very murky here.

Trees are beautiful things that clean the air, absorb rainwater. We’re happier around them. Cities need them. Trees can also be deployed for safety reasons, such as to separate cyclists and pedestrians from cars. Instead, cities built streets with “clear zones” that include not just shoulders but bike lanes and auxiliary lanes in them. We have intentionally designed cities that place cyclists in precisely the space we want errant vehicles to go, for them to be “safe.”

When it comes to cars, engineers can’t just say “this is your designated space, this space is not yours.” A 5.8-foot-wide car needs a lane that’s 9-15 feet wide, for buffer. A four-lane arterial street in the city, which has say two driving lanes and another two lanes for parking, could be 30-feet wide, but then the “clear zone” adds say ten feet in each direction, totalling 50-feet. Most cars have only one person in them, the driver. The driver’s ass might only be a couple feet wide, but the city gives them 50 feet (one 15-foot lane for driving + one 15-foot lane for parking + one 10-foot clearance zone on either side)!

Car lanes take up way, way more space than cars take up.

So when the topic of congestion relief arises and we’re all looking for ways to efficiently free up space, we need to peel back some of our assumptions behind how our world is designed. Seen from this way, encouraging modes of transportation that don’t take up extra space is of critical importance.

Most bike lanes in Toronto aren’t even real bike lanes, there’s just a certain amount of buffer space or the “clear zone” between car lanes and the sidewalk that arises naturally, and we paint a stencil of a bike in there and call it a “bike lane.” Bikes are narrow! They aren’t clunky. Unlike cars they are slight and don’t need much more room than they take up, a major tactical advantage when considering how people can move quickly all at the same time.

At least three people can fit shoulder to shoulder on a sidewalk, which is much narrower than a car lane and doesn’t require a “clear zone.”

Marshall’s focus on clear zones here was about safety, and that’s pertinent too, but it also nicely illustrates the wasted space we give cars. The point is to shrink the gap between how much space a physical thing takes up and how much space cities give it.