What indicates a legal speed while driving on the expressway?

A legal speed on the expressway is indicated by a speed limit that matches the flow of traffic. This concept is important because driving at a speed that is consistent with the flow of surrounding vehicles promotes safety and reduces the risk of collisions. If drivers go significantly slower or faster than the common speed of traffic, it can create hazardous situations, such as sudden lane changes or rear-end collisions.

While minimum speed limits and maximum speed limits provide guidelines for acceptable speeds, they do not necessarily reflect the ideal speed for safety in real-time conditions. It's important for drivers to adapt their speed based on traffic flow, road conditions, and other factors in order to maintain safe driving practices. Therefore, matching the flow of traffic while staying within established limits ensures that drivers are adhering to safety norms and regulations on the expressway.