Gwangju (광주) is a city in South Korea.
East towards Busan, Suncheon, Tongyeong
Option 1: Take a bus nr. 500 to five tombs place. You'll see the main road from the bus stop, just follow the sign to "Gwangju IC". The road to the toll gate is straight.
experience summer 2018: I went there and failed to catch a ride after waiting for over 1 hour there with a sign in Hangeul. I looked good, it may have been sheer bad luck. I ended up asking drivers at the petrol station across the street to bring me to a service area/tollgate. Eventually after half an hour of talking with my phone's translator to them one man drove me to the tollgate towards Daegu. I then found a trucker who took me all the way. Beautiful scenery. The issue with this spot is that there was little space for drivers to pull over safely.
Option 2: Use a Korean navigation app (Naver Maps is very good and available in English) to find a bus to take and get off at a stop in the Northeast of the city nearby the petrol station at these coordinates: 35.211149, 126.945946 (link to OSM). Cross the road onto the side where the petrol station is, and follow the pedestrian walkway back to a small intersection, where the bisecting road to the right has the highway going across it by means of a bridge. Squeezed between the main road you've come from with the bus and the elevated highway you'll see another road almost in front of you: Take this one and simply follow it. It's an emergency/service highway off-ramp directly behind the toll gate for traffic going East, and you can simply access the highway by walking it up. It's got road blocks on top of it so don't worry about traffic. Due to the toll gate there's plenty of space to stop, and indeed some trucks take their rest break here. In June 2019, Raureif and his girlfriend hardly waited five minutes with a sign saying "Suncheon" in Korean when a truck driver waived them over and took them all the way to Yeosu.
There is a really good spot on the northeast of the city, quite far from the city center but the cars go really slow and there is a big space for stopping. It is near the ramp, not in the highway, so you are legal there. The spot here. Got a ride in 20 minutes.