This two-lane highway was part of Interstate 85, which served as the main entrance and exit to the city of Atlanta. Most vehicles would use this stretch of road to travel to and from the city, however, when word of the outbreak reached everyone, civilians used both sides of the highway trying to evacuate the city. With everyone trying to get out and the military beginning their bombardment on Atlanta, the highway became gridlocked, trapping all vehicles and their occupants. With walkers everywhere, people either died on the highway in their cars or attempted to flee on foot, leaving their belongings in their cars.
Since the survivors left Atlanta, they used this stretch of highway to try and get to Fort Benning. However, they come to a stop when they found the highway blocked with several abandoned vehicles; and to make matters worse, Dale's RV breaks down due to his radiator hose, stranding them on the highway for quite some time.
While scavenging the vehicles for supplies, a herd of walkers pass by on the highway. Rick Grimes tells everyone to hide underneath the cars until the group of undead pass, however, Sophia gets the unwanted attention of two walkers. She runs off the highway towards the woods nearby to avoid the walkers that are pursuing her. However, she was not found.
While part of the group goes out to look for Sophia, Dale and T-Dog stay behind to repair the RV and await Sophia's return. Since T-Dog had cut his arm badly on a wrecked car when hiding from the herd, Dale goes and scavenges some cars in effort to look for antibiotics for him. Once the other group encounters Maggie in the woods, Glenn, Daryl, Carol and Andrea head back to the highway. Nearing sunset the remaining group at the highway discuss what to do next. Daryl offers to stay behind in the RV to make a sign and leave supplies for Sophia. Dale also offers to remain at the highway, as does Carol and Andrea. Dale then tells Glenn to take T-Dog to Hershel's farm and to find out whats happening.
Daryl couldn't sleep due to hearing Carol cry. He decides to go and continue to look for Sophia at night and Andrea goes with him. Not being able to find her, Daryl and Andrea emerge near the highway and head back to Dale's RV.
The group decides to leave the highway and join the rest at Hershel's farm since the search for Sophia seems to be less and less likely to find her or her returning to the highway however, they leave a message for her and some food and water in case she does return. Shane, even though was injured and had a hard time walking, volunteered to drive up and down the highway in an effort to find Sophia.
After Hershel's Farm got overrun by walkers, Rick, Carl, and Hershel come back to the highway. The survivors soon regroup and decide to head east. Soon later, they take the supplies and depart from the highway.
The highway is referred to as the Dahlonega Highway/Route 9 by Merle in "Killer Within". This is likely an oversight, as the real Route 9 is to the north of Atlanta, whereas Hershel's farm and the prison are near Newnan and Senoia, which is to the south of Atlanta (as is Fort Benning).
The cars seen in this highway were too low for the survivors to fit under so they decided to use "soccer mom" cars and trucks instead during filming to allow the actors to fit underneath.
Around 100-150 cars were used for the highway jam.
The actual location of the highway is Highway 20 in Hampton, Georgia, not far from Atlanta Motor Speedway.
The vehicle jammed highway is featured in the opening credits of Season 3 and Season 4.
The movie "Zombieland" also featured a vehicle jammed highway filmed at the exact same location.
The highway was also used in the episode "Rock in the Road" though its unclear if its supposed to be the Vehicle Jammed Highway or not.
Despite all of the corpses in the cars, no one appeared to have reanimated even though their brains were not destroyed.