Final answer:
The worst mistake at a red light when making a left turn is assuming oncoming traffic will stop, which could lead to an accident. Not signaling or turning into the wrong lane are also mistakes but are less dangerous than misjudging oncoming traffic.
Step-by-step explanation:
In the context of waiting at an intersection to turn left when the traffic light has turned red, the worst possible mistake you can make is to assume oncoming traffic will stop so you can finish your turn. This assumption can lead to a serious accident, as oncoming traffic may not stop in time, and you will be turning into their path. It is important to remember that when the light is red, all vehicles must stop, and it is illegal to enter the intersection to complete your turn.
While not using your turn signal may result in a ticket, and illegally finishing your turn in the right lane instead of the left can also be dangerous and illegal, the assumption that oncoming traffic will stop is potentially the most dangerous because it increases the risk of a collision. Traffic signals are meant to control the flow of traffic and ensure safety at intersections, thereby reducing accidents.