The 2023 Maui wildfires not only devastated communities, they also exposed the dangers of those that lacked enough evacuation routes.
Neighborhoods that are only accessible by a single road, also known as “one way in, one way out” neighborhoods, were the focus of a special HPR series on fire vulnerability in 2024.
Now, new research has aimed to address the question: how many exit routes is enough to save lives during a fire? According to University of California Santa Barbara researcher Cat Fong, six seems to be the magic number.
Cat Fong is the lead project scientist for the Wildfire Resilience Index, which she helped build and develop by using her training in geospatial mapping to assess wildfire risk and resilience in different areas.
Fong spoke with HPR about her experience combing through California's Redbooks, which provide detailed wildfire activity statistics by jurisdictions, and news articles to compile the names and locations of every wildfire death in America since 2008, and what that research has taught her.
Interview Highlights
On the optimal number of evacuation routes for a community
CAT FONG: We tabulated all of the wildfire fatalities that we could find in the last 20 or so years in the U.S., and we assigned all of those fatalities to a community where those people lived, and then for each of those communities we were able to count the number of major roads that intersected with the boundary of that community… and we found a threshold at around six roads, where once you hit six or fewer roads, the cumulative rate of per capita fatality starts to increase exponentially. And so what that means is that there's this threshold, which is a very useful policy heuristic of six roads. Six roads or fewer, and you likely do not have enough exits in the event of a wildfire. More than six roads, so seven or more, and continuing to add roads accrues no more additional benefit, and so that very steep threshold is probably the most important finding of this paper.
On why 6 roads is the ‘magic number’ for evacuation routes
FONG: The example that I would point to when I think about this stuff is the Camp Fire, and what happened in Paradise. Paradise has six major exits, so it's right at that threshold for risk, and if you read the after-incident reports for what happened in Paradise, there was construction that was causing delays and lane closures. There were burnover events where the fire crossed over and blocked roads, and so there were roads during the evacuation process that were not usable, and I think that that's just a reality. When you’re going to have an evacuation, you're going to get congestion, you're going to have burnovers, you're going to have debris, you're going to have accidents. And so I think that having six roads builds in a level of redundancy that can help build resilience and buffer that community from being egress limited.
On the Wildfire Resilience Index
FONG: We've mapped about 30,000 communities in the U.S., and you can interact with the dashboard, you can find your particular community where your friends and family live… and it will tell you where you fall in the exit vulnerability. So, do you have six or fewer exits? Do you have seven or more exits? And then it will also tell you what hazard classification you're in. So is your burn probability low, medium, or high? I think this is a really useful way for citizens, community members, local city planners to better understand what the risk landscape is for themselves. And then if you are somebody who makes these kinds of decisions at a state level, like for the state of Hawaiʻi, or for us, for the state of California, you can compare across the different communities and try to identify what places need prioritization. ...
This was the single hardest thing I've ever done as a researcher. … It was emotionally devastating to go through and read about the people who died, and to just understand that this is a place where the people who are dying are the old and the vulnerable and the young, and that this is a preventable outcome.
More information about the Wildfire Resilience Index can be found here.
This story aired on The Conversation on June 4, 2026. The Conversation airs weekdays at 11 a.m. Jinwook Lee adapted this story for the web.
