Speed limits on limited access highways, freeways, and expressways vary between states. But all states have one speed law in common.
Look at the following question:
What is always a safe speed on a limited access highway? 20 mph? 40 mph? 60 mph?
The simple answer is that no speed is safe at all times. Or, in other words, a posted speed limit of 65 mph does not always mean 65!
You are always required to drive at a speed that is reasonable and prudent under the circumstances, conditions and actual and potential hazards.
This requirement is known as the basic speed law or general speed law.
Remember, a posted maximum speed limit shows the fastest speed you may drive under ideal conditions. When the weather is bad or there is a lot of traffic, you must slow down. It is always unlawful to drive at a speed which endangers the safety of persons or property.
What is a safe speed? A safe speed is the speed that allows you to have complete control of your vehicle and avoid actual and potential hazards.
Several questions on your test will ask you about situations when you must adjust your speed. Excessive speed is often the factor that turns a minor incident into a fatal crash. It is also the most important cause of car skids.
While excessive speed is a main factor in crashes, driving too slowly is also dangerous. Some highways have minimum speed limits, where slow speeds can impede traffic flow or be dangerous. You may only drive slower than the posted minimum speed limit when conditions require it (the basic speed law).