A four lane highway was present outside Hill Valley in 1986.
On May 14, 1986, Marty McFly and Einstein used this highway as a secluded location for temporal displacement as they traveled back to 1931 in the DeLorean Time Machine. He arrived on June 13, 1931, where Danny Parker was chasing Kid Tannen's henchmen in his police car. The DeLorean, which had appeared between the two vehicles, slowed Danny down enough for the criminals to escape. The DeLorean's rear louver vents activated, blinding Danny and running his car off the road.
Later that day, Kid Tannen kidnapped Doc Brown and made his escape in a stolen police van, driving down the highway. Marty, holding onto the van, used a tire iron to dislodge a spare tire that was blocking his route. He later dropped the tire iron, which disappeared into the night.
In the timeline where Emmett married Edna Strickland, the Hill Valley South Gate could be found on the highway, part of a wall that surrounded the entire town.