Final answer:
The two vehicles should turn left as planned, passing each other passenger side to passenger side, following standard traffic rules for safety and efficiency.
Step-by-step explanation:
When two vehicles are approaching each other and are both signaling to turn left, they should turn in front of each other so that their passenger sides are beside each other. This is a common driving rule meant to ensure safety and efficiency at intersections. The correct action for the vehicles is to turn left as planned, ensuring that they mutually pass each other on the side where their passengers would be seated, which is on the right-hand side in countries where driving is on the right. It is important for drivers to adhere to the standardized traffic rules to maintain order and prevent accidents.