Interstate Highways Facilitate the Flow of Firearms Used in Crimes

The movement of firearms between states is a major contributor to gun crime, injury, and death in the United States. Guns used in crimes move routinely between states along multiple major transportation routes, a phenomenon termed the “iron pipeline,” especially about Interstate 95. According Columbia University Mailman School of Public Health researchers, other “iron pipelines” exist throughout the country, playing a significant role in the interstate transfer of firearms used in crimes. The findings are published in JAMA Network Open.

The researchers sought to identify possible gun trafficking routes along the interstate highway system, the site of one-quarter of all vehicle miles traveled in the U.S. Using publicly available interstate gun trace data from the Bureau of Alcohol, Tobacco, Firearms, and Explosives, they measured interstate transfers of firearms used or suspected to have been used in crimes from 2010-2019. Creating 48 separate datasets, one for each destination state of interest, the researchers compared the count of guns used in crime traced to interstate purchases for states with interstate highway connections and states without these connections.

“We hypothesized that counts of traced firearm transfers between states connected via major interstate highways would be greater than what we might expect based on their population sizes and geographic proximity, and that traced gun transfers would be greatest along the Interstate 95 (I-95) corridor,” said Christopher Morrison, PhD, assistant professor of Epidemiology at Columbia Mailman. “Understanding how guns flow around the country is important for identifying trafficking routes, and the impact that each state has on its neighbors.”

The results show that between 2010 and 2019, 526,801 guns used in crimes in the lower 48 of the United States were traced to interstate purchases and that multiple interstate highways were involved in this gun flow. The researchers discovered previously unidentified “iron pipelines” throughout the country and determined that gun traffic along the I-95 corridor is more complex than previously recognized.

Earlier research by the authors demonstrates that the inflow of guns from other states undermines local gun supply-reduction strategies, ultimately draining limited resources and contributing to the overall burden of gun crime in the U.S. This new work suggests there may be a synergistic relationship between interstate connection and gun law strength in determining trafficking patterns.

From 2010-2019, 275,345 people died and 803,393 were admitted to emergency departments due to interpersonal shooting events. In 2019 alone, over 30,000 guns traced to in-state and interstate purchases were used in violent crimes such as assault, robbery, and murder. In addition to the direct impacts of gun crime on health and safety, exposure to violence can have lasting impacts, including psychological effects and increased risk of cardiovascular disease and premature mortality.

“Our study showed that interstate gun flow has critical implications for gun violence prevention, as gun transfers across state lines can undermine local gun control policies,” noted Morrison, who is also affiliated with the School of Public Health and Preventive Medicine at Monash University, Australia. “By identifying highway routes regularly used for the transfer of guns used in crimes, this study provides law enforcement and public health authorities with critical areas for intervention. Our data offer valuable insights into the origins of interstate crime guns, a key public health intervention point. We conclude that national policies and inter-state cooperation are needed to address this issue.”

Co-authors are Leah Roberts, Brady Bushover, Ariana Gobaud, Christina Mehranbod, and Carolyn Fish, Columbia Mailman School of Public Health; and Mark Hoofnagle, Washington University School of Medicine.

The work was supported by the CDC National Center for Injury Prevention and Control (grant R49CE003094) and the New Jersey Center on Gun Violence Research at Rutgers University.