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.