Coolant temp gauge goes to hot in traffic but fine on highway

Highway means air flowing through the radiator from vehicle speed. Traffic means the radiator fan is supposed to do that job. Your radiator fan is either not turning on or not spinning fast enough. Check the obvious first: is the fan actually spinning when the temp is high? If not, it could be the fan motor (about 80 bucks), the fan relay (10 bucks), or the coolant temp sensor that tells the fan to kick on (15 bucks).

On 8th gen Civics (2006-2011), the radiator fan relay is a very common failure. It is in the under-hood fuse box. Swap it with another identical relay in the box to test. If the fan starts working, you found your 10 dollar fix. Also check that the radiator is not clogged with bugs and debris blocking airflow.