The Sign to Slow Down
According to California Vehicle Code 21452, yellow lights warn that the vehicles facing the signal will soon be shown a red indicator. Whether a circular yellow light, or a left arrow yellow light, vehicles must heed the warning of the yellow light as a transition from a green light to a red one.
Some drivers interpret yellow lights as a chance to speed up and "make" the light before it turns red and passing through the intersection is illegal. Though many do this, it is not always the safest choice. A vehicle who enters the intersection during a yellow light is allowed to pass through with out penalty, but attempting to catch the yellow light and passing into the intersection when the light has just turned red, is not allowed. This is why slowing down for a yellow light, and waiting for the red, is often the safest approach to reading a yellow indicator.
There are times, however, when continuing through a yellow light is preferred. If a car is traveling with a momentum which makes slowing and breaking for the yellow light difficult, or if the vehicles is in the intersection when the yellow light is indicated, then stopping for the yellow light would be a bad choice. Maintaining the appropriate speed limit is always important when entering an intersection, whether the light is green or yellow.
Pedestrians also must heed the yellow light indicator. If a person traveling on foot is a facing the circular or left arrow yellow light, the light is showing that there is not enough time for the pedestrian to cross the road. Attempting to begin crossing during the yellow light is illegal, unless a pedestrian control signal shows otherwise.
Drivers must use their best judgment about whether or not to enter an intersection during a yellow light, as doing so is important in preventing accidents and injuries.
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