As a two-lane road, Alligator Alley suffered from poor construction and environmental planning. It was also notorious for high-speed accidents including both head-on collisions and collisions with wildlife. The need to improve the road was one of the factors considered in the decision to reroute I-75 onto Alligator Alley, which was rebuilt as a four-lane Interstate highway between 1986 and 1992. Many bridges and culverts designed to let water and wildlife pass underneath the roadway and permit the natural flow of the Everglades’ waters were built as part of the upgrade. This helped to reduce the environmental impact of the highway somewhat, especially upon the severely endangered Florida panther. The completion of the converted Alligator Alley was the final link of the I-75 extension. The segment was signed Interstate 75 on November 25, 1992, completing the highway from Miami to Sault Ste. Marie, Michigan.