To understand temperature rising mainly in slow traffic, compare it under normal, safe conditions: cold versus warm, idle versus steady speed, and light versus higher load. Note whether temperature falls once road speed increases and whether the A/C is on. Change one condition at a time so the result stays useful.
Do not create a risky test just to reproduce it. Check for fan operation only from a safe distance and inspect for obvious coolant loss when cold.
Quick educational note
For information, not a diagnosis or repair instruction. Vehicle-specific checks are still required. Consult the manufacturer's guidance and a qualified technician.
How to use this information
This article explains general principles and does not establish what is wrong with your vehicle. Read the content limitations.