Interstate 81, traffic and air pollution: Experts analyze highway teardown’s effect on residents

A recent lawsuit that threatens to halt the teardown of the Interstate 81 viaduct in Syracuse raised questions about the project’s effect on traffic and air quality for city residents. 

A judge will ultimately rule on Renew 81 for All’s lawsuit based on whether the state followed environmental review regulations. But the lawsuit’s claims provoked community questions about those impacts. 

Central Current interviewed experts, including one who said he has conducted one of the only studies on the impacts of tearing down highways to replace them with boulevards. That’s the plan in Syracuse.

The lawsuit’s plaintiffs, including Onondaga County Legislator Charles Garland, said they are concerned the community grid will lead to increased traffic that would worsen air pollution on the South Side. The highway has forced harmful emissions on majority Black neighborhoods for decades, Garland and other plaintiffs have argued.

Garland’s claims are contradicted by the New York State Department of Transportation’s projections. The DOT’s review expects traffic and emissions to decline.

How the I-81 project could affect traffic in Syracuse

University of Connecticut civil engineering professor Norman Garrick said he and his colleagues conducted one of the only studies — if not the only study — examining the effects of tearing down highways and replacing them with boulevards in multiple communities, in 2011.

There hasn’t been much research because few highways have been replaced by boulevards, and little traffic data exists for the ones that have been, he said.

Garrick and his colleagues found tearing down cross-city highways cut traffic on three replacement boulevards by at least about 30%. 

“One of our tasks was to understand what happened to the traffic,” Garrick said. “And we really weren’t able to fully account for why this occurred, but there is a lot of theory as to what happens with traffic when you remove a freeway.” 

Garrick said he and the two other colleagues believe that traffic rerouted, or people used other modes of transportation. 

The study suggests Renew 81 for All’s claims that traffic will continue increasing as the state tears down the viaduct are wrong. Garrick labeled that claim to be “ludicrous.”

Traffic overall across the country has increased over the last several decades because the U.S. government built highways that incentivized sprawl, Garrick argued.

But the DOT studies concluded that segments of highway leading into the community grid will see reductions in traffic, particularly south of the city.

Right now, I-81 supports about 70,000 car trips per day just south of downtown Syracuse. That would decrease to less than 25,000 car trips if the community grid is built, according to DOT projections. 

Garrick studied three highways: the Embarcadero in San Francisco, the Central Freeway in San Francisco and the Park East Freeway in Milwaukee. All three had enough data for Garrick and his team to review traffic volume before, during and after the replacements. 

The Embarcadero and Park East Freeway were replaced by integrated boulevards that allowed access to other streets in the city. 

The Embarcadero saw traffic decrease 51% while the Park East Freeway saw traffic drop by 63.5%. 

The Central Freeway, which was replaced by a limited access highway, saw a decrease in traffic by 31.5%.   

Garrick pointed out that where the traffic went is unclear. In the case of the Embarcadero, side streets around the boulevard saw a big jump in traffic. Car volume on those streets increased about 44%, the study showed. The area is mostly a commercial district, Garrick said. 

In Milwaukee, traffic volume on streets around the new boulevard increased 5.4%. Traffic volume on nearby freeways actually decreased about 6%, the study showed. 

The streets that often see increases in traffic are commercial districts with destinations for drivers, Garrick said. 

Boulevards did not lead to increased congestion in any of the three cities Garrick’s team studied, even where there were increases in traffic.

Traffic congestion is typically a problem in areas that already have congestion. Proper signage can prevent or reduce traffic backups, Garrick said. 

“The idea that traffic is going to increase, that makes absolutely no sense on the face of it,” Garrick said. “Yes, we can say that we cannot predict the future. All evidence would suggest that does not happen.” 

How the I-81 viaduct’s removal could affect air quality

A key factor in whether the community grid reduces air pollution will be how much diesel traffic the grid sees, said Doug Brugge, a public health professor at the University of Connecticut. 

“The amount of diesel is going to have a huge impact,” Brugge said. “If it really is true that they make a boulevard and the trucks go around a different way then that’s going to reduce pollution a lot.” 

Diesel fumes typically come from trucks. The DOT studied truck traffic as part of its analysis of the community grid and other alternatives. The DOT expects the new traffic pattern will redirect 16-24% of truck traffic at most peak times from the 81 corridor.

Even more truck traffic would be diverted southbound on I-81 south of the city. In the morning, DOT projects the community grid project would divert 69% of truck traffic in the morning and 38% in the afternoon.

DOT found that the amount of diversion is not “substantial” enough to require hotspot analysis of pollutants.

However, it did do some testing because of community concerns. The additional testing and analysis found that concentrations of particulate matter, a pollutant linked with respiratory and cardiovascular conditions, would decrease between about 10 and 30 percent on the southern side of the viaduct with the community grid.

Diesel exhaust can include particulate matter and other chemicals that have been linked to respiratory illnesses and asthma. The Environmental Protection Agency labeled fumes from diesel trucks carcinogenic, meaning exposure can create a greater risk for cancer. 

Research has shown that diesel traffic can disproportionately contribute to poor air quality. 

A 2021 study by researchers from the University of Virginia highlighted that diesel-exhaust exposure plays a major role in why communities of color have disproportionate exposure to nitrogen dioxide. 

Though diesel-fueled traffic accounts for only about 5% of traffic in major American cities, it contributes to about 50% of nitrogen dioxide pollution, according to the study. 

Low-income neighborhoods and communities of color are exposed to 28% more nitrogen dioxide than high-income and majority-white neighborhoods, the study found. 

A number of other factors in addition to diesel affect how emissions impact a community, including prevailing winds, meteorology, geography and buildings, Brugge said.

Reducing overall traffic volume would also likely improve air quality, Brugge said. If the same volume of traffic currently on the viaduct were dropped to street level, the pollution could increase, Brugge said. 

The DOT anticipates a community grid will produce less of all types of harmful emissions it measures. That includes carbon monoxide, nitrogen oxides, volatile organic compounds and particulate matter. 

Syracuse should look to mitigate air pollution near the highway, regardless of the plan for 81, Brugge said.

He suggested improving air filtration systems in the public housing next to the highway as part of Blueprint 15. 

“If there was something that could be done to reduce pollution in those homes, that would be something that seems like a good thing to do,” Brugge said.