**Speed competitions** on public roads are **prohibited** as a general rule. This is because driving at high speeds can be very dangerous. It increases the risk of making mistakes, as it is more difficult to react to unforeseen events and reduces the ability to see what is happening on the sides, a phenomenon known as **tunnel vision**. Additionally, driving fast for a long time can cause **fatigue and aggression**.

Competitions are only allowed if the **authorities authorize them** and the necessary measures are taken to ensure safety. Participating in unauthorized races can result in the loss of points on the driving license. Therefore, the correct answer is that speed competitions on public roads are not allowed, except for authorized exceptions.