In late August, TahoeCleanAir.org/Tahoe Sierra Clean Air Coalition released an independent Tahoe Basin Wildfire Evacuation Analysis, taking artificial intelligence (AI) and combining it with regional wildfire experience to create various simulations of what could happen in a real-life Tahoe Basin wildfire evacuation.

The Analysis’s findings show that Tahoe workers, residents, and visitors could face hours-long, potentially life-threatening slow evacuations in trying to leave the basin that could be further worsened with more development.

“The AI-generated Placer evacuation simulations reveal a nine to fourteen-plus hour evacuation time depending on road closure conditions. This is in stark contrast to the 2016 Placer County Environmental Impact Statement, which estimated evacuation time for the study area at 3.7 hours. Washoe Tahoe AI generated simulations include potential closures of SR28 at Stateline and Sand Harbor resulting in eight and nine hour wait times,” says the TahoeCleanAir.org press release about the Analysis.

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The 38-page Analysis was based on more than 400 wildfire evacuation simulations, drawing attention to the few roadways and “choke points” in the basin to hopefully bring awareness to public and governmental land-use planners of possible evacuation outcomes and take that into consideration in strategic planning like Placer County’s Tahoe Basin Area Plan (TBAP).

Tahoe land planning agencies, emergency responders, and fire crews have been talking about the Analysis since it came out, and the Lake Tahoe Fire Chiefs Association recently released a 185-page Lake Tahoe Regional Evacuation Plan in which 24 agencies weighed in. The document, dated September 10, 20204, is open for public comment for the next two months.

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In response to TahoeCleanAir.org Tahoe Basin Wildfire Evacuation Analysis, the Placer County Sheriff’s Office (PSCO) said, “The Placer County Sheriff’s Office and our partners are aware of a report that was released raising questions about evacuation times in the Tahoe Basin. We want to assure the public that in Placer County we have evacuation protocols that we train through and utilize regularly.”

“The Placer County Office of Emergency Management has conducted numerous AI scenarios using the same software utilized in this report. The Placer County Office of Emergency Management clearly understands how outcomes can differ vastly by simply manipulating data prompts. We worked with the same simulation software company used by the report vendor to add in specific tools, such as contra flow, and that data indicates we can evacuate much faster than the vendor illustrates in the simulations,” says PCSO Communication Manager Elise Soviar.

No-Notice Versus “Planned Event” Evacuations

In the Analysis, the TahoeCleanAir.org models provided hypothetical “no-notice” versus “planned event” evacuation simulations.

“Fire experts use the term ‘no-notice’ for an emerging incident that poses a sudden and immediate threat to human life but may still involve evacuation orders. Historically, no-notice evacuations have overwhelmed emergency responder resources and defied the rapid implementation of emergency operation plans,” TahoeCleanAir.org explains.

The PCSO responded saying while the Analysis acknowledges it “does not account for all the potential evacuation scenarios”, it does not consider the methods used to evacuate, such as its systematic evacuation process which first gets residents in immediate danger to safety, then rolls out evacuations in phases. 

“The scenarios illustrated in the report, according to the vendor, is an entire Lake Tahoe and surrounding area evacuation order all at one time,” says Soviar, which she thinks is unlikely. Little to no-notice evacuations happen in denser, rural communities, and Soviar doesn’t remember a big wildfire in Placer ever being on a “no-notice” evacuation order. “Even with the Mosquito Fire, people had plenty of notice.”

The Mosquito Fire was considered the largest wildfire in California in 2022 which ignited during a September heat wave and burned 76,788 acres in dense forest. Foresthill was the most impacted; it took the population of 11,000 people about three hours to evacuate. “The odds of something like that [a no-notice evacuation] are very low,” she says.

Doug Flaherty is a former southern California Fire Combat Battalion Chief who hired PyroAnalysis LLC and Ladris AI to generate the evacuation scenarios used in the Analysis. He believes the most recent “no-notice evacuation” was the Caldor Fire.

“That was the poster child for how things can go wrong. Fire officials will tell you off the record that the response for that fire was not successful. It was successful in that no one got hurt, but they caught a lucky break in the weather.”

He says, “even with the diminished population [after the evacuation warnings were sent out], they still had significant back up in traffic. If the fire wasn’t curtailed by the shifting winds, then the outcome could’ve been worse.”

Choke Points and Contraflow

On page 8 of the Analysis, Flaherty explains contraflow, a traffic management strategy that increases the capacity of roads by reversing the traffic flow of one or more of the lanes.

“The implementation of contraflow requires a large number of personnel and may not be able to achieve its intended outcome during no-notice evacuations when the availability of first responders is limited,” the Analysis states.

“AI evacuation modeling software estimated potential evacuation times based on a variety of road closures that create choke points. These bottlenecks could reasonably be expected during a fast-moving wildfire evacuation in peak summer tourist season, which coincides with peak wildfire season,” TahoeCleanAir.org further states.

How Soviar explains it, she agrees that contraflow refers to changing traffic patterns so it all goes in the same direction, doubling or tripling the capacity of vehicles that can get out. (They worked with the same AI software to manipulate traffic flow inputs, which generated a different result.) There’s the assumption that traffic controls stay normal (ex. stopping at red lights) rather than having personnel out there ushering people through and no mention of buffer zones, places like the Tahoe Meadows where people can shelter in place.

She says in the report’s most extreme example, a 14-hour evacuation time in South Lake Tahoe, the data assumed that people would be stuck in traffic from the far west end of the South Shore all the way to Stateline, not taking in account that people were out of harm’s way of the wildfire long before that.

The Alert System

“Smoke and panic impact the efficiency and safety of wildfire evacuations, creating considerable challenges for both evacuees and emergency responders,” reads the Analysis, page eight.
In the event of a wildfire, local police agencies generally assist fire departments in communicating evacuations by going door-to-door. If people refuse to leave, they note that. Reverse 911’s go out via landlines and cell phone alerts.

All Placer County patrol vehicles are equipped with High-Low sirens and its Unified Command works closely with the fire departments.

Soviar says that “cell phones have changed the game” in being able to communicate with people, and local agencies consistently post maps and real-time information about power outages and changes.

“There are a lot of tools you can utilize even if you don’t have power,” she says.

The Analysis states, “When mobile networks fail, first responders’ and government agencies’ ability to disseminate emergency alerts and updates is severely hindered.”

It’s true that a quickly moving wildfire can cause heightened panic and people start overloading the cell towers. During the recent Davis Fire, Washoe County lost cell service for a bit but within half a day the Lake Taho Fire Protection District worked with three major providers—Verizon, AT&T, and FirstNet—to bring in mobile towers to be able to manage the higher volume.

“There’s no single alert system when communications go down,” Doug Flaherty says.

A Call for Better Land Use Planning

It’s no secret that several Tahoe residents are frustrated with land-planning agencies who seem to be pushing for development and increasing population density in the basin, which seems to be one of the main factors in creating this report.

“This analysis underscores the need for Tahoe policy makers to provide better, more transparent public safety planning. Officials need to take a reality-based approach to land use planning decisions to help avoid issues experienced in other major wildfires,” the independent report said.

TahoeCleanAir.org is currently challenging Placer County on its TBAP (Tahoe Basin Area Plan); an excerpt from its Verified Petition for Writ of Mandate submitted to the court notes, “The Town Centers in Placer County were set up in the 2016 TBAP EIR with a great deal of community involvement. Placer County’s TBAP amendments, however, incentivize growth outside of Town Centers, which directly conflicts with the 2016 EIR for the TBAP.”

“I’ve been reaching out to the agencies for three years now and some have been involved in the publication of this Analysis. Unlimited height standards on buildings were passed by the TRPA just recently and it’s frustrating for the community.

“No one has ever said we’re opposed to amendments of the Plan; we just want them to do their due diligence to provide a cumulative Environmental Impact Report that includes a roadway capacity assessment. All we asked for was for supplemental EIR’s…We absolutely believe that there will be more life loss due to development if the agencies continue to ignore this,” Flaherty says.

Thoughts From the Davis Fire

Doug Flaherty has lived in Incline Village for the past six years. When asked if the recent Davis Fire has changed his view of the Analysis (evacuation simulations on pages 26-29 focus on the East Shore), he talked about how he felt that it furthered the need for a further roadway by roadway capacity assessment and take a closer look at how significant impact projects could be mitigated.

“We want [Tahoe land managers] to transparently publish a roadway by roadway capacity evacuation assessment. I just did it for $100,000; it’s not that hard,” Flaherty says. “Washoe County assigned 1.5 cars for each household evacuating in six hours, but we think there’s more than that. We’re going to assign background traffic.”

“It brought to light very real and demonstrated threats. The Davis Fire caused the Mt. Rose Highway to be shut down, which was in our Analysis. Placer County was trenching Highway 28 but thankfully they shut it down due to a wind shift. Even with east prevailing winds, that still forces Crystal Bay residents to Spooner. That would’ve been catastrophic.”

North Lake Tahoe Fire Protection District Chief Ryan Sommers said that CAL FIRE has conducted more realistic planned evacuation drills for Incline Village based off past fire behavior, taking into consideration the topography of the area in wildfires burning up slopes, not across them like in a “V” pattern. He noted that the Analysis does not consider the extensive fuels reduction work that has been done on the East Shore.

“With the extensive fuels reduction work that has been done, we have a better chance of suppressing a fire before it becomes a newsworthy scenario,” Chief Sommers says. “The Davis Fire was stopped in a fuels-treated area.”