How we analyzed California's wildfire evacuation routes
REDDING, Calif. (AP) — How many roads are enough to get out?
That's the question we wondered after watching tragedy unfold in Paradise, California, last year during the Camp Fire.
Paradise had five two-lane roads and one four-lane road leading out of town. But the fire forced officials to close three of those routes, further clogging the remaining roads.
Did Paradise have an unusually high ratio of residents to escape routes ? Or were other California communities in a similar situation?
A USA Today-California Network analysis of California communities and evacuation routes shows that some areas in the state are far outside the norm when it comes to the number of lanes of roadway available for the size of the population.
This is a shorthand method of evaluating the efficacy of egress routes, according to emergency planning experts.
To evaluate exit routes for Californians living in areas at risk of a fire-related evacuation, we combined and analyzed data from the U.S. Census Bureau, Cal Fire and OpenStreetMap.
We took 2010 census block-level populations, combined with Cal Fire's "Fire Hazard Severity Zone" maps, and aggregated those to ZIP codes, then applied more current population estimates. Next, we spatially joined those areas with the fire risk map. That provided a current population risk breakdown for each ZIP code, based on area and estimated population.
We added OpenStreetMap data to each ZIP code, so we could see which roads cross into or out of the area. Combining the ZIP code population and fire risk data with the standard number of lanes for every major roadway allowed us to come up with a set of ZIP codes that have the greatest number of people living in the highest-risk areas and hypothetically trying to use the fewest number of lanes to leave in any direction or to areas at less risk for fire.
What does this tell us?
In short, the analysis gives an estimate of how many people there are for every lane of major road leaving an area.
When we looked at all ZIP codes in California that have people living in a very high fire risk zone, we found, on average, 134 residents living in the riskiest areas for each lane of traffic going either direction .
Only one out of 20 ZIP codes has more than 313 people living in the riskiest areas for each lane of traffic. Paradise had more than 1,000, putting it in the worst 1%. But some areas, such as Oak Park in Ventura County, South Lake Tahoe in El Dorado County or the Palos Verdes Peninsula in Los Angeles County, have two, three or even five times the number of people living in the highest-risk zones, per lane of major roadway out, compared to Paradise.
Here are the ZIP codes the analysis identified as being roughly within the worst 1% in the state when it comes to population-to-evacuation-route ratios:
90042: Highland Park and Eagle Rock in Los Angeles County
90272: Pacific Palisades in Los Angeles County
90274: Rolling Hills in Los Angeles County
90275: Rancho Palos Verdes in Los Angeles County
91935: Jamul and surrounding areas in San Diego County
92065: Ramona and surrounding areas in San Diego County
92131: Scripps Ranch in San Diego County
91320: From Newbury Park to Dos Vientos Ranch in western Thousand Oaks in Ventura County
91377: Oak Park, an unincorporated community in Ventura County
93021: Moorpark in Ventura County
92548: Homeland and areas northwest of Homeland in Riverside County
92584: Menifee in Riverside County
92314: Big Bear, Minnelusa and Sugarloaf (92386) in San Bernardino County
93924: Carmel Valley and Jamesburg in Monterey County
95954: Magalia in Butte County
95969: Paradise in Butte County
96150: South Lake Tahoe and surrounding areas in El Dorado County
95634: Georgetown and surrounding areas in El Dorado County
94508: Angwin in Napa County
94708: Cragmont, Kensington and La Loma Park in northeastern Berkeley in Alameda County
95422: Clearlake in Lake County
95451: Kelseyville in Lake County
95631: Foresthill and surrounding areas in Placer County
95666: Pioneer, Barton and Buckhorn in Amador County