Major highway expansion projects are significantly contributing to the intensification of urban heat islands, according to new research from Northeastern University.
By analyzing satellite-based temperature data from 11 major expansion projects in the San Francisco Bay Area, researchers found that these developments have a measurable impact on local temperatures.
The study, which tracked projects between 2013 and 2020, found that highway work—ranging from adding new lanes to installing guardrails—accounted for 70% to 88% of the increasing heat disparity observed in the region.
Mitigating heat impacts
Serena Alexander, an associate professor at Northeastern University, said the findings highlight the need for better urban planning.
“I’m not trying to argyue we shouldn’t build highways,” Alexander said. “We have to be aware of these impacts and where we can mitigate [them].”
While highway construction is often intended to ease traffic congestion, Alexander noted that traffic levels frequently return to pre-construction levels as more drivers use the new lanes.
Despite these challenges, highway infrastructure remains a massive area of investment. As of January 2026, the American Road and Transportation Builders Association reported nearly 115,000 new highway projects underway in the U.S., backed by $257 billion in federal funds.
The research focused on California because the state has seen rapid highway expansion due to population growth. Between 2018 and 2023, the California Department of Transportation added 550 lane miles.
Alexander believes the findings likely apply to other metropolitan areas with similar expansion models.
To reduce these temperature spikes, researchers suggest integrating more plant life into urban areas and establishing green buffers, such as grass and shrubs, along highway corridors.