Speed **competitions** are **completely prohibited** on any type of road, including highways, unless authorized by the authorities and necessary measures are taken to ensure safety. Participating in unauthorized races can result in the loss of points on the driving license. This is because driving at high speeds increases the risk of accidents, as it is more difficult to react to unforeseen events and the ability to see what is happening on the sides is reduced, a phenomenon known as **tunnel vision**.

Therefore, the correct answer is that it is not allowed to engage in speed competitions on highways.