Take a minute and consider the following question:
What is always a safe speed on a freeway? 40 mph? 50 mph? 60 mph?
The simple answer is that no speed is safe at all times.
This applies to all roads. You should remember that a posted speed limit of, as an example, 55 mph does not always mean 55!
This is known as the basic speed law or general speed law. It is common for all states (just the wording is slightly different). This law means that you may never drive faster than is safe for current conditions.
A posted maximum speed limit shows the fastest speed you may drive under ideal conditions. When the weather conditions affect stopping distances and visibility, you must slow down. If road or traffic conditions may create a hazard, you must slow down. It is always unlawful to drive at a speed which endangers the safety of persons or property.
In other words, you can drive the speed limit and still be guilty of driving too fast.