A more thorough explanation:

Definition: Reasonable speed refers to the safe speed at which a driver can operate a vehicle, taking into account various factors such as weather, traffic, road conditions, visibility, and the condition of the vehicle. It may be lower than the posted speed limit and should never exceed it.

For instance, California Vehicle Code § 22350 states that drivers should not drive at a speed greater than what is reasonable or prudent, considering the weather, visibility, traffic, and the width and surface of the road. If a driver exceeds the reasonable speed limit, they may be cited for speeding or found to be negligent, even if they were driving within the posted speed limit.

For example, in the case of Meyst v. East Fifth Avenue Service, Inc., the Alaska Supreme Court ruled that a driver was not driving at a reasonable speed, even though he was driving within the posted speed limit. The driver failed to apply his brakes when he saw an oncoming car in his lane because that car was going around a wrecker crew in the opposite lane. This failure to slow down and take into account the other vehicle's presence was deemed unreasonable and negligent.

Another example of unreasonable speed is when a driver is driving too fast for the road conditions, such as during heavy rain or snow. In such cases, the driver should slow down to a speed that is safe for the conditions, even if it is lower than the posted speed limit.