A low level area outside of Freedom City. Head south from Any Port until you reach the end of the road, then head west until you begin "Traveling". Once you arrive in the chemical plant, head nw across the bridge (note: a little south of here are the screech and iron liver mutations, and further south are comparatively strong mobs) and follow the path until you're "Traveling" again. When you arrive at Edith's house, try to head w and s as much as possible until you're "Traveling" again. This will take you to the abandoned highway.
A detailed map with descriptions can be found here.