No Escape In Sight - 1990 Tennessee I-75 Pile-Up
Car accidents happen every day around the world for a wide plethora of reasons. Most of them are caused by driver error; and some of them are, unfortunately, fatal. But when Mother Nature plays a role in a car accident, her actions can cause unparalleled devastation.
Such was the case on U.S. Interstate 75 near Calhoun, a small Tennessee town located between the cities of Chattanooga and Knoxville. Thousands of vehicles use the highway daily, and this day was no exception. Little did anyone realize, but a combination of corporate nonfeasance, inadequate safety measures and a rare weather phenomenon would, on one fateful day, cause one of the most catastrophic car accidents in American history.
Interstate 75 is one of America’s busiest highways. Stretching from Miami to the Canadian border north of Detroit, I-75 is a major commercial thoroughfare that serves as a pillar in the ground transportation network. With such large volumes of traffic, accidents are bound to happen. With that being said, if there’s any road network in the world that’s capable of safely moving millions of vehicles per day, it’s the American interstate system. But, with traffic moving at speeds upwards of 70 miles per hour, accidents on the interstate can be extremely dangerous, if not fatal.
On the morning of December 11, 1990, things didn’t seem particularly unusual for commuters driving on Tennessee’s I-75 in the forests near the Hiwassee River. However, at about 9:10 A.M, a thick fog suddenly appeared over the highway, reducing visibility to near-zero to both northbound and southbound traffic. The first collision occurred when one semi rear-ended another that had slowed down in the dense fog. While the unhurt drivers got out to assess the damage to their rigs, a car rear-ended the back of the second semi, which was then rear-ended by another semi; starting a massive chain-reaction crash. On the other side of the highway, a northbound automobile rear-ended another car that had also slowed down in the fog, causing a chain reaction to start in the northbound lanes of the interstate.
By the time the fog, smoke and fires cleared, 99 vehicles had become part of the rubble on I-75. 12 people were killed, and at least 42 more were injured. To this day, the Calhoun crash remains one of the deadliest car crashes in American history.
The National Transportation Safety Board (NTSB) of America was called in to investigate how the disaster occurred. Their report would uncover some disturbing findings that led Tennessee residents to question whether or not I-75 was even safe to drive on.
Fog was obviously the most major contributor to the tragic crash. The chain-reaction pile-ups occurred because drivers couldn’t even see what they had hit, let alone be able to react in time to avoid the calamity. In addition, drivers reacted differently in the adverse situation—some slowed down, some pulled over and stopped altogether, while others continued full speed ahead.
Fog is a common weather occurrence, especially in this part of Tennessee. But big accidents like this are much rarer. In addition, there was something unusual about the fog on that day—it was extremely thick, and rolled in almost instantly. The fog caught drivers off guard, which is unusual in most fog-related incidents. So why was this fog so severe?
The answer to that question was a weather phenomenon known as a temperature inversion. Normally, the air that’s the closest to the ground is warmer than the air higher up in the atmosphere. A temperature inversion occurs when a warm air mass passes over top of the ground and disrupts the normal convection cycles in the atmosphere. As a result, the air temperature below the warm air mass is actually colder at the lower level. This results in water vapour, smoke, and other pollutants getting trapped under the warm air mass; causing a very thick fog to settle in the low-lying areas.
On the morning of December 11, 1990, the conditions at the accident scene were perfect for an inversion to occur. Between Knoxville and Chattanooga, I-75 runs through an area known as the Cumberland Plateau. In the basin of the plateau, where the highway is located, cool air tends to get trapped if a warm front passes directly over the highlands. Meteorologists determined that this is exactly what happened in the days leading up to the crash. Not only did this itself cause fog to form, but it also trapped the vapours coming from both vehicle traffic and the evaporation from the Hiwassee River and its surrounding marshes. Combined, these two natural phenomena played a major role in the Calhoun accident.
While there was never any doubt that fog is a naturally-occurring problem on that particular stretch of I-75, scientists were skeptical that the amount of natural evaporation in the area could cause such a dense fog that was reported on the day of the accident. People began to suspect that the paper plant owned by Bowater, one of the largest newsprint manufacturers in the world at the time, had contributed to the accident.
Large-scale paper plants, such as the Bowater plant in Tennessee, put out huge amounts of pollutants as part of the paper-making process. Not surprisingly, the massive clouds that billow out of the smokestack often result in fog formation in areas near the plant.
In addition, paper plants use a lot of water, which then has to be discharged somewhere. Bowater dealt with their wastewater by building a series of wastewater containment ponds around their Tennessee plant. One of these ponds, Pond #4, was located directly beside I-75. Due to its large size and contamination with particulate materials, it was speculated that evaporation from Pond #4 also played a major role in the formation of fog on the day of the crash.
Engineers were able to calculate the evaporation rates from the bodies of water in the area, including Bowater’s containment ponds. They were also able to determine the amount of vapour emissions coming from the plant around the time of the accident. Their conclusion: while a certain amount of naturally-forming fog occurs in the area, the most significant contributions to the fog on that day came from Bowater’s operations.
Although the devastating Calhoun crash was somewhat of an anomaly, fog had been a significant issue along that stretch of I-75 since the day it opened. Several smaller chain-reaction accidents had occurred prior to the 1990 crash, so it was well-known that the highway could be dangerous. The State of Tennessee thought they had solved the problem by putting up warning signs and flashing lights that alerted drivers to potential fog hazards. However, on the day of the crash, those signs weren’t working properly, leaving drivers with no idea of the danger ahead.
When the NTSB released their report into the accident in 1992, it was clear that the catastrophe was almost inevitable. A perfect storm of adverse weather, industrial activity and insufficient safety warnings left those involved in the December 11, 1990 crash with little chance of avoiding catastrophe.
Bowater denied any responsibility for the accident; claiming that the fog on that day was natural and that the State of Tennessee should have taken more safety precautions. However, it was discovered that Bowater was in possession of a report made decades earlier that implicated Bowater activity in the formation of unusually dense fog in the region. With lawsuits impending, Bowater settled out of court with the families of the victims and the State of Tennessee. They later shut down their Tennessee operations, and became defunct in 1997.
The State of Tennessee also settled with the families, and took steps to ensure a similar tragedy would never happen again. A computerized fog detection system was installed to alert drivers of adverse road conditions. Using massive, programmable overhead signs, the system alerts drivers of the conditions ahead and can reduce the highway speed limit accordingly. Freeway interchanges feature massive swing arm-type gates which close the freeway on-ramps to traffic in the event of extreme fog. Advances in vehicle technology have helped, too.
Despite the fact that many changes have been made, many area residents still believe, however, that I-75 is still unsafe. They know that, despite our advances in technology and understanding, that Mother Nature is still a savage beast that will always threaten to strike the interstate once again.