Paint peels off an I-81 viaduct. Credit: Michael Greenlar | Central Current

Along the future community grid, the New York State Department of Transportation will plant trees to beautify the streets — but they could also serve another purpose. 

Landscaping will help “soften” and enhance the look of the concrete noise barriers along between Colvin Street and Dr. Martin Luther King, streets that cross Interstate 81, said Elizabeth Parmley, who leads the I-81 project in Syracuse. 

However, one environmental expert said that, if done right, vegetation can provide a second line of defense for the community against both noise and air pollution. 

The trees will be planted after the viaduct project is completed. The viaduct is expected to close around the end of 2026. The project is estimated to complete sometime in 2028. 

The city plans to plant more than 30 different species of tall-growing trees that provide plenty of shade, officials said. Typically, about two-thirds of the selected species are native to Syracuse.

Vivek Shandas, an environmental and climate science professor at Portland State University with experience working on urban sustainability projects in upstate New York, said that the structure of a tree can help reduce certain noise frequencies and air pollutants, mitigating some environmental harm. 

“What we’re finding is that, as those trees mature and become better, stronger, [they are] more able to intercept particulate matter, more able to absorb some of the nitrogen dioxides, improve the air quality, more able to reduce noise,” he said. 

The six most-common air pollutants in cities include particulate matter, nitrogen dioxide and lead. Tree leaves and needles absorb nitrogen dioxide in its gaseous form while particulate matter deposits on the surface of the needles. The more leaves or needles on a tree, the better it is to absorb these air pollutants. 

Tree sizes and ages will matter. Planting younger, smaller trees may not be the most effective. 

“If they’re small trees, they will have a marginal effect on noise or air pollution,” Shandas said.

Studies have shown that trees can help reduce noise levels by 5 to 10 decibels, depending on the density and structure of the trees. Reduced noise pollution can lead to reduced cortisol levels, ultimately having a positive impact on public health, Shandas. A study in Portland showed that an increase in tree canopy lead to nearly 6% decrease in asthma hospitalizations locally. 

Tree-lined neighborhoods and business districts also have an impact in reducing urban heat islands caused by dark, impervious surfaces such as roads and rooftops, city officials said. Shade from trees helps mitigate the heat in street corridors and parking lots where temperatures are often 10 to 20 degrees higher than nearby green spaces. 

Shandas pointed out a seasonal dynamic that will play out, however. Deciduous trees, which shed their leaves in the fall and winter, lose the primary mechanism of trapping pollutants in those seasons. 

To overcome this problem, the state’s Department of Transportation will plant a mix of deciduous and evergreen trees, Parmley said, which will help retain vegetation across the seasons.   

Trees along traffic-heavy urbanized areas often “live fast, die young” after being inundated by stress factors like heat, air and noise pollutants, Shandas said. 

After the state plants the trees, the city will be tasked with watering, pruning and caring for them. 

A contractor will plant the trees with a two-year warranty. After the two-year warranty, the trees will become part of the city’s tree pruning cycle. The city prunes trees two or three years after planting, continuing the process until it reaches maturity. After trees are mature, the city prunes them every four to seven years, depending on species and site conditions. The city also replaces trees that may be lost to age, environmental stress from vehicles or vandalism. 

The city provided the state with feedback on what plantings are favorable, said Joe Driscoll, the city’s liaison to the state for the I-81 project. 

Tree maintenance is incorporated into the city budget. However, the city has not yet projected costs for canopy maintenance near the community grid, a city spokesperson said.

“The cost is really about what you’re trading off,” Shandas said, “… it ends up making up for itself in the public health benefits that emerge.”

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Debadrita Sur is a multimedia journalist and Report for America corps member who reports on the I-81 project and public housing for Central Current. In 2023, Sur graduated with a master’s degree in journalism...