Trees Make Streets Safer

By Ryan McGreal
Published September 22, 2006

Want to make a street safer? Plant rows of trees along its sides.

For years, traffic engineers have insisted that trees make streets more dangerous for motorists, as do narrow lanes and obstructions like parked cars. Unfortunately, this theory does not stand up to empirical scrutiny.

Eric Dumbaugh of Texas A&M investigated accident records and drew conclusions that contrasted sharply with the engineering dogma:

Though engineers generally assert that wide clear areas safeguard motorists who run off the roads, Dumbaugh looked at accident records and found that, on the contrary, wide-open corridors encourage motorists to speed, bringing on more crashes. By contrast, tree-lined roadways cause motorists to slow down and drive more carefully, Dumbaugh says.

In all the areas Dumbaugh studied, the wide, unobstructed roadways that traffic engineers prefer were associated with statistically significant increases in vehicle crashes, whereas the presence of trees and concrete planters alongside the road significantly reduced the crash rate.

Dumbaugh explains that trees provide visual cues to drivers about their speed and send strong signals about the potential for collisions, encouraging drivers to slow down and drive more safely.

Of course, trees also create a physical barrier between motorists and pedestrians, provide cooling shade on hot days, absorb exhaust, produce oxygen, and even extend the life of pavement.

In other words, design elements that make the streets safer for drivers also make the street safer for pedestrians. It's time for traffic engineers to revise their models in the light of the evidence.

Ryan McGreal, the editor of Raise the Hammer, lives in Hamilton with his family and works as a programmer, writer and consultant. Ryan volunteers with Hamilton Light Rail, a citizen group dedicated to bringing light rail transit to Hamilton. Ryan wrote a city affairs column in Hamilton Magazine, and several of his articles have been published in the Hamilton Spectator. His articles have also been published in The Walrus, HuffPost and Behind the Numbers. He maintains a personal website, has been known to share passing thoughts on Twitter and Facebook, and posts the occasional cat photo on Instagram.


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By jason (registered) | Posted September 22, 2006 at 11:03:02

this is a no-brainer. Drive down Main Street and then Graham Avenue. Or for a more equal comparison - 2 residential side streets: one with and one without trees along the edge. The difference in our natural response is quite amazing. I find the same is also true of streets with homes and buildings built closer to the sidewalk as long as there is a narrow 'traffic right of way'. For example - Florence Ave near Victoria Park or Pearl Street North. Compare them to a typical south Mountain residential street. Street width and the 'built environment' including trees, make a huge difference in driver behaviour.

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By Locke (registered) | Posted September 22, 2006 at 13:59:50

It has long been acknowledged that people slow down in built up environments. In particular, I've read about this phenomenon in relation to highways where motorists will slow down in areas of many overpasses, close buildings or walls, etc. Think 403 under King, Main and Aberdeen; traffic slows down entering this area and then takes off again on leaving.

If we know this, and we know that speed and accident frequency and severity are linked, it would indeed seem 'a no-brainer' that trees would help slow down traffic and prevent serious accidents.

The reality is, traffic engineers were first trying to increase the effectiveness of moving cars and secondly making sure there were as few things in the way when cars inevitably sped off the road.

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