Excessive-speed laws vary by state. But generally, there are three types of speed-limit laws:

• “absolute”
• “presumed,” “presumptive,” or “prima facie,” and
• “basic.”

The available speeding-ticket defenses depend on what type of speeding law you’re accused of breaking. Here’s some general information about absolute, presumed, and basic speed laws.

“Absolute” Speed Limits

Absolute speed limits are straightforward: If you exceed the posted speed limit, you’ve broken the law. For example, California’s “maximum speed limit” law sets the absolute limit for most highways at 65 miles per hour. So a California motorist who drives faster than 65 miles per hour will generally be guilty of speeding, regardless of how safely the motorist was driving.

“Presumed” Speed Limits

Presumed speed limits (also called “presumptive” and “prima facie” limits) aren’t as simple as absolute speed laws. When you get caught breaking a presumptive speed limit, the judge will presume you’ve broken the law. But you can still fight the ticket by proving your speed—though over the presumed limit—was safe considering the conditions.

Take Texas, where the prima facie limit is 30 miles per hour on urban-district streets. An officer might ticket a Texas driver for going 32 miles per hour in an urban district, but that doesn’t necessarily mean the driver is guilty of speeding. By convincing the judge that 32 miles per hour was a safe speed because, for example, traffic was light and the weather was good, the driver might be able to beat the charge.

“Basic” Speed Laws

Basic speed limits prohibit driving an unsafe speed—typically, no presumptions or specific limits are involved. For example, the basic speed laws of New York and Florida make it illegal to driving at a “speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing.”

With basic speed laws, a motorist can generally be convicted of speeding even for driving slower than the posted limit—it just depends on what’s safe under the circumstances. In determining whether you were going a safe speed, a judge or jury might consider:

• how much traffic there was
• how much faster than the posted speed limit (if there was one) you were going
• what the weather was like (for example, whether it was sunny and clear or dark and rainy)
• whether you were on a curve or cresting a hill
• whether there were pedestrians around, and
• whether you were approaching an intersection, crosswalk, or other types of crossing.

But the facts of every case are different. So there’s no exact formula for determining what qualifies as a safe speed.