Vehicle traffic as a determinant of community firearm violence.

BACKGROUND: Urban design sets the conditions under which individuals encounter one another. It is modifiable and can be an important intervention point for firearm assault prevention. Higher vehicle traffic, a previously under-studied exposure in firearm injury research, may contribute to firearm violence by fostering spaces that create interpersonal encounters while hindering positive social processes. We aimed to examine the association between vehicle traffic and firearm injury risk within the city of Portland, OR. METHODS: In response to local community concerns, we investigated the relationship between vehicle traffic volume and firearm assault risk in Portland, OR using novel traffic estimates from Streetlight, Inc, and firearm injuries from Portland Police, 2019-2021. We examined this association using (1) cross-sectional logistic regression with clustered standard errors and time strata covariates, and (2) an ecological case-crossover with conditional logistic regression comparing injury months to matched control periods at the same location in both the previous and subsequent months at the same type and time of day. Analyses were repeated at tracts and street segments in a high-risk neighborhood. RESULTS: Portland experienced 585 firearm assault injuries from 2019 to 2021. Tract-level average daily traffic volumes ranged from 9,584 to 230,804 trips. Tracts with 10,000 higher vehicle trips were associated with 27% increased risk (RR: 1.27, 95% CI: 1.12-1.45) of firearm assault, controlling for time variables and clustering standard errors at the census tract. In the case-crossover analysis a one standard deviation increase in traffic was associated with 59% (OR: 1.59, 95% CI: 1.17-2.17) and 85% (OR: 1.59, 95% CI: 1.35-2.55) higher odds of firearm assault at the same type and time of day in the prior month and subsequent month respectively. Street-segment analyses were in the hypothesized direction but not statistically significant. CONCLUSIONS: Innovative strategies to curb firearm violence are necessary today more than ever. Future research should investigate whether traffic control could be a new avenue for community firearm violence prevention.