What does a solid red traffic light signify?

A solid red traffic light signifies that drivers must come to a complete stop and wait for the light to turn green before proceeding. This rule is essential for maintaining road safety and ensuring the orderly flow of traffic. When a red light is displayed, all vehicles and pedestrians must halt to prevent collisions with cross traffic that may be moving through the intersection on a green light.

The other options suggest actions that could compromise safety and violate traffic laws. Proceeding with caution, speeding up to clear the intersection, or turning left when the light is red, unless otherwise posted, can lead to accidents and are not permitted under Illinois traffic regulations. The clear directive of stopping at a red light is critical to protecting all road users.