Alcohol negatively affects drivers' ability to **perceive traffic signals**. When a person consumes alcohol, their vision is impaired, making it difficult to correctly interpret signs and traffic lights. This is because alcohol primarily affects the **brain and eyesight**, reducing the ability to clearly see the surroundings.

Additionally, alcohol causes a **false sense of security** in the driver, which can lead to risky decisions and mistakes that increase the risk of accidents. There is also a **greater difficulty in coordinating movements** and a **slower reaction** to unforeseen situations.

Therefore, under the effects of alcohol, drivers have a diminished perception of traffic signals, which can seriously compromise road safety.