The trees give a visual break to drivers so they can focus on their side of the road better. | Photo courtesy of Dhanix/Wikimedia Commons
Driving down Houston highways is a little greener than the rest of the state.
Houston is the leader in planting trees alongside highways, according to the Texas Department of Transportation, the state agency that manages highways. Greenery alongside highways improves public safety by reducing pollution and breaking up the monotony of driving, according to experts.
TxDOT hopes by the end of 2020 to have planted 2 million trees alongside highways in the Houston district as part of the department’s Green Ribbon Project, spokesperson Deidrea George said. The goal is to plant another million trees by 2030.
The Green Ribbon Project began in 1999 to restore natural beauty alongside Texas’ highways by turning concrete-dominated landscapes into ribbons of green.
As TxDOT gears up to expand Interstate 45 in the coming years, planting trees remains a part of the department’s plan to mitigate impact.
‘Highway hypnosis’
Part of the reason trees are planted alongside highways is to improve highway safety by giving a visual break to drivers.
“It allows drivers’ concentration to be broken a little bit from getting that highway hypnosis,” said Bert Cregg, professor of horticulture and forestry at Michigan State University.
Cregg is working with Michigan Department of Transportation to add shrubbery and grasses alongside highways in suburban Detroit.
Trees, wildflowers and shrubbery are all effective at giving visual interest to highways to help prevent highway fatigue, Cregg said.
Drivers in suburban areas drove 3 mph slower if trees were present, according to a study published by the Institution of Transportation Engineers.
Other benefits to planting trees near highways are they can prevent engine exhaust from spreading and add greenery to areas that usually lack it.
University of Minnesota Department of Forest Resources professor Gary Johnson said when an area loses trees, there comes a spike in those having respiratory problems.
Challenges
While roadside greenery does provide aesthetic and safety benefits, it also adds other challenges for transportation engineers.
With greenery comes wildlife seeking shelter and food. Small mammals crossing highways become more common once trees are planted alongside highways.
“We tend to think of wildlife as a good thing,” Cregg said. “But people might want to swerve and miss them. That could be something else raised as an objection.”
Nuts, fruits and limbs from trees also add debris to the roadway. Strong rainstorms loosen the soil around trees and make it easier for them to collapse onto roads.
While trees do help with storm water runoff, Cregg said, soil erosion caused by trees remains a bigger concern.
