In some states, you've violated the law if you drive even one mile above the posted speed limit. In other states, it is presumed that the posted speed limit is the safest top speed, but a driver cited for speeding may have the opportunity to prove otherwise. When given a speeding ticket, it is easier to defend your actions in a "presumed speed limit" state, particularly where you were only driving a few miles above the posted speed.
Absolute Speed Limits
Speed limits were originally intended to provide motor vehicle drivers with an idea of what speed was deemed to be wise and reasonable for that particular road under clear and dry road conditions. Initially, speed limits also served as evidence that the basic speed law was violated, but over time, speed limits in some states became "absolute speed limits," and any speed over the posted speed was a violation.
When a driver is charged with exceeding a posted speed limit in a state with an absolute speed limit, the prosecution is required to prove that the driver was driving at an excessive rate of speed and that no greater speed than the one posted was permitted at the time and place of the violation.
Presumed Speed Limits
In "presumed speed limit" states, a driver is presumed to be breaking the law by going above the posted speed limit, and it's the driver's burden to prove that he or she was going at a safe speed for road and traffic conditions. The following are examples of basic speed laws used in presumed speed limit states:
- In California, no person shall drive a vehicle upon a highway at a speed greater than is reasonable or prudent having due regard for weather, visibility, the traffic on, and the surfaces and width of, the highway, and in no event at a speed which endangers the safety of persons or property.
- In New York, no person shall drive a vehicle at a speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing.
- In Pennsylvania, no person shall drive a vehicle at a speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing, nor at a speed greater than will permit the driver to bring his vehicle to a stop within the assured clear distance ahead.
Such laws are not viewed by courts as unconstitutional, even though they shift the burden of proof to the motorist, because, rather than creating a conclusive presumption of unreasonable speed, they merely create a rebuttable presumption , which the driver may overcome by providing evidence showing the reasonableness of his or her rate of speed.
In such states, the prosecutor is required to prove beyond a reasonable doubt that the driver's speed was unreasonable under the circumstances. It is not necessarily enough for the prosecution to establish that the driver exceeded the posted speed limit, even though mere speed may constitute a violation of the basic speed law.
In most jurisdictions, the prosecutor is aided by an evidentiary rule providing that proof that an individual has traveled at a rate of speed in excess of the posted speed limit constitutes prima facie proof of a violation of the basic speed law.