History's A Disaster

1990 I-75 Fog Disaster

• Andrew

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A perfectly ordinary Tuesday morning turned into a wall of white and the worst commute of many people’s lives. We dive into the 99-car pileup on I-75 near Calhoun, Tennessee—how a fog-prone valley, river-backed reservoirs, and nearby industrial ponds set the stage for sudden zero visibility, and how human reactions at different speeds amplified a single impact into a chain of catastrophe. It’s a forensic tour through weather, geography, and the split-second choices that define disaster.

We walk you through the minutes that mattered: the first semi slowing in the southbound lanes, the unseen trucks ahead, the Oldsmobile crushed and burning, and the eerie progression as drivers entered from clear air into chaos. Then the response: the first deputy stumbling past the wrecks to call in help, triage sites on the median, hazmat teams managing peroxide-fueled fires, and a multi-agency push that saved lives while the pileup grew. The human side meets hard logistics here—sirens in the fog, coordination across counties, and the grind of clearing a corridor that looked like physics gave up.

From there, we pull on the threads of accountability. The NTSB pointed to speed variance in sudden low visibility, but the report also flagged systemic failures: flimsy warning signs, no automated detection, no ramp controls. We revisit contested studies around Bowater’s settling ponds, a temperature inversion that day, and a settlement that acknowledged harm without conceding sole blame. Most importantly, we chart the fixes that finally worked: Tennessee’s $4.5 million fog detection system with visibility sensors, radar, CCTV, variable speed limits, and swing gates to lock down ramps when sight distance collapses. Since its launch—and a 2006 upgrade—this stretch hasn’t seen another fog-fueled mass crash.

If you’re drawn to transport safety, disaster history, traffic engineering, or just the anatomy of how small failures become big ones, this story delivers detail, context, and hard-earned lessons. Hit play, then tell us what you’d change first: driver behavior, industrial practices, or smarter infrastructure? Subscribe, share with a friend who loves history and engineering, and leave a review to help more curious listeners find the show.

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Special thank you to Lunarfall Audio for producing and doing all the heavy lifting on audio editing since April 13, 2025, the Murder of Christopher Meyer episode https://lunarfallaudio.com/


SPEAKER_00:

Tuesdays are great. You made it past Monday, and you're now one step closer to the weekend. But you still gotta get up way too early though. Get dressed, hop in your car, and deal with traffic and everyone else wondering why the hell they're up this early. What could be better than that? Well, maybe add in some fog. Because fog always makes everything better. You're flying down the highway, then all of a sudden it's like someone throws a blanket over your windshield. You can't see a damn thing, so you slam into the idiot ahead of you who decided to stop. Don't worry though, you're not alone. Because the guy flying up behind you is about to tap that ass too. And really, is there a better way to start today? Just ask the commuters on Interstate 75 in Tennessee who hit a sudden fog bank and found themselves involved in one of the largest auto wrecks in history on Tuesday, December 11th, 1990. So, what happened? I'm Andrew, and this is History's A Disaster. Tonight, we're driving into the I-75 fog disaster that resulted in a 99-car pile-up just outside the small town of Calhoun, Tennessee. And tonight's episode is brought to you by Polka Bob's Music Center. Polka Bob is currently running a surprise fire sale on accordions and xylophones. So come on down and say hi to Polka Bob. You can squeeze his accordion and bang his xylophones before deciding to take one home today. Jeez, that's not creepy at all. Why was he winking at me when he handed me the ad to read? I need better sponsors. I-75, which runs from the Canadian border in Michigan all the way down to Miami, Florida, is the second longest north-south interstate after I-95. It runs through six different states for just under 1800 miles. So, obviously, there's gonna be some shitty spots on the highway. And one of them just happens to be outside Calhoun, Tennessee. This 10 mile stretch of I-75 lies 70 miles southeast of Knoxville and runs from mile marker 29 to 39. This stretch is in two separate valleys surrounded by ridges within the ridge and valley Appalachians. Appalachians. The area has a lot of creeks that run through these valleys that flow into the Hiawassee River, a major river that cuts the area in half near where the interstate crosses. The Chickamauga Dam, not far downstream from the area, creates a reservoir which backs up into this section of the river, making large lakes near the interstate where these creeks all meet up with the river. Also in the area is the Bow Water Paper Mill. The mill is just outside of Calhoun, close to the interstate and sitting on the banks of the river. At the time, Bow Water owned land on both sides of the interstate and operated wastewater treatment settling ponds next to it. Now these settling ponds, and if you've ever driven past the factory or a plant or anything, everyone's seen them, they're the little lakes that sit out front. They're part of a large system and it's used to help separate solid pollutants from wastewater. Water flows into these ponds and the heavy solid shit settles to the bottom of the pond over time and the cleaner water flows out. It's part of a whole system, and the system really has nothing to do with the accident other than these ponds. So, anyways, all that to say it's a low-lying area with lots of cold air and a ton of water in the area. Put all that together and you got the perfect recipe for fog soup. Thick, nasty fog soup that can pop up in the area at any time without warning. If you live in the area or regularly drive through here, like truck drivers, at some point you got caught in this shit and have some kind of fog story. Since this section of Interstate opened up in 1973, there have been multiple accidents here. The first of which happened just within three months of the opening and involved 18 vehicles, three deaths, and 10 injuries. And this was just the first of many. So to help cut down on accidents in the area, they put up a sign which read Extreme Dense Fog Area, next five miles, along the stretch in both directions. The sign contained flashing lights that would activate if fog was detected. So, yep, they put up a blinky light on a sign that most people aren't gonna pay attention to anyways. Especially when the lights flashed non-stop for three days, like they did in the southbound lane prior to the accident, or just didn't work at all like the northbound lanes. And they put these signs up after another 18 vehicle accident occurred in 1979. And since they put these signs up, there was no major accidents at all throughout the 80s. Although I highly suspect they had more to do with the Tennessee Highway Patrol than the stupid blinky lights. On foggy days, troopers would sit at the end of the foggy area and well seeing a cop sitting, everyone's gonna slow down. So there's that. The Highway Patrol would also do routine fog checks in the area. Which brings us to December 11th of 1990. During their early fog checks at 5.30 and 8 o'clock, Highway Patrol noted no fog in the area. However, by 9 a.m. the fog started rolling in. Visibility was dropping as the miles ticked by and the fog grew thicker, dropping from 20 feet to 10 to barely seeing past the hood of your car. At 9.10, a semi traveling in the southbound lanes carrying daikumo peroxide in separate tanks slowed to 35 miles per hour. Unfortunately, the semi unseen in the fog ahead of them had slowed to 25 and was rear-ended just 100 feet south of the State Route 163 overpass. The truck drivers got out and attempted to check for damage and bullshit for a few minutes before a 91 Oldsmobile sedan smashed into the rear of the chemical semi. Before anyone could move, the Oldsmobile was crushed under the semi and set on fire when it was rear-ended by another semi. Neither the driver or the passenger of the Oldsmobile made it out of the car. This was the first, but far from the last cluster of accidents in the southbound lanes. At 9.15, the first accident happened in the northbound lanes when an 87 Ford Escort slammed into an 87 Honda near the overpass, which in turn was rear-ended by an 83 Toyota pickup, which was then hit by a 1990 Pontiac, which was then in turn hit by an 89 Oldsmobile. Surprisingly, no one was injured in this mess. As the minutes ticked by, the stopped commuters could hear the sounds of impact, the screech of brakes, the crunching of metal on metal, the secondary explosions as fuel tanks ignited. Some slowed or stopped to try to see what was happening. The stopped or slowed moving vehicles invisible in the fog, waiting to be struck by drivers still traveling at a high rate of speed. Within minutes of the first accident, both directions of the interstate had become a tangled nightmare of wreckage spanning hundreds of yards. Vehicles were crushed, stacked, thrown into positions that seemed to defy physics. Tractor trailers jackknifed across multiple lanes. Cars were smashed down to fractions of their original size, wedged beneath larger vehicles or sandwiched between them, and still more vehicles kept coming. Drivers emerged from clear conditions into fog with zero warning, finding themselves suddenly confronted with walls of stop traffic and wreckage. Even those who managed to break couldn't stop in time. It was far too late. The pile of wreckage just grew larger. Ten minutes after the first collision, the final accident occurred. Accidents in the southbound lanes involving 72 vehicles would stretch for a fifth of a mile north of the overpass. The northbound lanes, a total of 27 vehicles would be involved in multiple accidents stretching a quarter mile south of the overpass. The first 911 calls started coming in as the first northbound accident happened. Within minutes, Bill Dyer of the Bradley County Sheriff's Office was on scene. Being the first on scene, he originally completely missed the first accidents in the fog. He had to turn around and drive back to find the scene. When he got back to the area, a seriously injured man stumbled out of the fog and towards his cruiser. When he exited the cruiser to help the man, he could hear the metal-on-metal sounds of multiple accidents just north of his location. As he got closer, the screams of the wounded got louder. After seeing what he could of the devastation, he immediately called for backup in emergency services. Over 200 first responders would end up on site from as far away as Chattanooga and Knoxville. By 9.30, the Tennessee Emergency Management Agency began coordinating the response between the 33 different departments who answered the call for help. Within minutes, the Tennessee Highway Patrol had the highway shut down on both ends. McMaine County EMS set up triage in the median north of the overpass to evaluate the wounded as they were pulled from the wreckage. While Bradley County EMS set up another triage site to the south. 42 survivors were treated for injuries ranging from minor cuts and scrapes up to more traumatic injuries that required hospitalization. The injured would be transported to hospitals as far away as Chattanooga and Knoxville. In total, eight people died in the fires raging across the wreckage, and four more had died as a result of injuries sustained in the crash. Firefighters from multiple departments worked the fires that had spread throughout the area. Most concerning was the presence of chemical tanks containing peroxides that were sending flames 30 feet in the air. Special hazmat teams had to be called in to deal with the chemicals and potential spills. While they all worked quickly and were able to get all the injured out within 45 minutes, it would be hours before they were able to open a single lane in either direction. Clearing all the wreckage away would take several days. The NTSB investigation that followed was forced to rely on eyewitness accounts, police reports, and aerial photography to reconstruct the accident since the cleanup and reopening the highway prevented them from doing the reconstruction on site. It would be years before they released their findings in 1992. In their report, they placed the blame on the drivers for responding to the sudden loss of visibility by driving at wildly different speeds. They also identified other major safety concerns that helped play a part in the pile-up, along with their recommendations to deal with the issues. Recommendations that included the installation of a fog detection system and a system to warn and slow drivers through the area when fog is present. The report also stated that the settling ponds and steam from the bow water plant and other nearby plants may have played a role in the formation of the fog, but they stopped short of outright blaming them. Some meteorologists blamed the fog on the day of the accident to a temperature inversion since there had been a rapid 32-degree temperature change from the day before. Most people though leaned towards it being Bow Water's fault. There had been a study done previously in 1979 of the area that pointed at the Bullwater ponds being a major factor in causing fog in the area, but the study called for further research and study of emissions coming off the ponds to determine this. While a study was eventually funded, it never happened. And it had absolutely nothing to do with Bullwater possibly using political pressure to squash the study. Not to worry though, because Bowwater conducted their own study later in 1979. And come on, there's nothing suspicious at all of a company investigating themselves after squashing an outside investigation. And while they did find that the ponds contributed somewhat to the fog, they would never say exactly how much. And I wonder why. However, the Department of Energy concluded in their study in 1981 that the Bow Water ponds made the presence of fog three times more likely. Strange that the Bowwater study didn't mention that at all. Bowwater would continue to deny any responsibility for the fog that formed and instead claim that the dense fog had been a natural occurrence even before they had opened up and began running operations in the area. They would also go on to accuse the state of Tennessee of failing to implement necessary fog detection and warning equipment along that stretch of I-75, which technically, yeah, they are right on that. Slapping up a couple of blinky lights don't really cut it sometimes. But they would also go on to agree to an out-of-court settlement of$10 million, which comes out to about 19 million in today's money. With 44 victims and family members of victims in January of 1994, they also agreed to limit the usage of the 235-acre pond closest to the interstate. Which, sounds like to me, some shitheads at Bowwater had a guilty conscience. And a lot of people agreed with Bowwater's criticism of Tennessee Department of Transportation for failing to put into place a proper fog detection system after the accidents in the 70s. Tennessee's DOT eventually paid$800,000 to settle lawsuits calling them out for negligence of conditions in the area. As a result of the collision, they would go on to institute several safety measures along this section of highway. The section of I-75 between mile markers 31 and 39 was designated as a fog advisory zone or a fog advisory area, which contains large warning signs on both sides of the road in both directions that warn commuters when they are entering and leaving the area. They also repainted this section with extra paint markings and reflectors to make it more visible. A$4.5 million computerized fog detection system was installed in 1993. This system monitors three miles of the highway north and south of the Hawassi River with 9 forward scanner visibility sensors, 14 microwave radar vehicle detectors, and 21 CCTV cameras. It is connected to a warning system that contains more blinky lights, electronic signs, and variable speed limits within the fog advisory zone, and electronic controlled swing gates which would block access to the interstate from the six entrance ramps in and near this stretch of the highway in the event of dense fog. This system automatically drops the speed limit from 70 to 50 miles per hour when visibility drops below a quarter mile and to 35 miles per hour when the visibility drops below 480 feet. And yeah, that all sounds great on paper, but really are people actually slowing down? We all know speed limits are just suggestions, anyways. And then the swing gates at the entrance ramps would turn on when visibility drops below 240 feet. This system started up in December of 93, and in 2006 it got a$6.6 million upgrade that added the video cameras. Since the system was put into place, no major multi-vehicle accidents have occurred along this stretch in foggy conditions. So, it works a hell of a lot better than a couple stupid blinky lights. And that was the 1990 i-75 fog disaster. Thanks for listening, and if you like the show, please consider leaving a rating or review on your app of choice, and you can reach out to the show at history is a disaster at gmail.com with questions, comments, or suggestions. As well as consider following the show on social media. We're on Facebook, Instagram, TikTok, YouTube, a few others, and share the episode. Your friends will love it. Also, take care of yourself out there. Chase that dream. Live for today. Because tomorrow is never guaranteed. Thanks and goodbye.