In the United States, the left turn signal is typically used for left turns, while the right turn signal is used for right turns. This convention is consistent across the country and is based on the International Traffic and Highway Signage (ITHS) standards, which are widely adopted in the U.S. and many other countries.

The reason for this standardization is to ensure clear and consistent communication on the roads. The left turn signal is activated when a driver intends to turn left, and the right turn signal is activated when a driver intends to turn right. This system helps to prevent confusion and potential accidents, as drivers and other road users can easily understand the driver's intentions based on the position of the turn signal.

According to the National Highway Traffic Safety Administration (NHTSA), the use of turn signals is a critical safety feature that helps to reduce the risk of crashes. In fact, studies have shown that the use of turn signals can reduce the likelihood of a crash by up to 20%. The consistency of the left and right turn signal convention across the U.S. contributes to this safety benefit by ensuring that all drivers are using the signals in the same way.

Additionally, the ITHS standards were developed with input from various stakeholders, including traffic engineers, law enforcement agencies, and driver education experts. These standards were designed to be intuitive and easy to understand, which is why the left and right turn signal convention is so widely adopted. The use of the left turn signal for left turns and the right turn signal for right turns is a clear and straightforward system that helps to minimize confusion and improve road safety.

In summary, the left turn signal is used for left turns and the right turn signal is used for right turns in the United States, following the ITHS standards. This convention is based on safety considerations and is designed to enhance road safety by providing clear communication between drivers and other road users.