Speeding tickets are easily the most common ticket issued in the United States. In every state, a traffic ticket can be issued to drivers who violate laws restricting the speed at which a vehicle may travel.

Generally, states carry two types of laws related to speed restrictions:

1. Laws that set specific maximum speed limits in certain settings. For example, a state may declare different maximum speeds at which a vehicle may be operated on a state highway (65 m.p.h.), on a residential street (35 m.p.h.), and in a school zone (25 m.p.h.).
2. Laws that require drivers to operate their vehicles at a speed that is reasonable under the circumstances. For example, even if the posted maximum speed limit on a rural highway is 65 m.p.h., driving on that highway at 65 m.p.h. in a torrential rainstorm at night could result in a speeding ticket, because driving at such a speed could be deemed unsafe based on the hazardous road and weather conditions.

There are essentially three types of speed limits being enforced around the country: “absolute,” “presumed” and “basic” speed limits. As you might imagine, the defenses differ for each one.

Absolute speed limits are the most common type of speed law. The sign will clearly state 55 mph, so if go 56 mph or faster, you have violated the law.

Presumed speed-limit violations are more nuanced. In states that use this system (Texas and California are examples) it’s legal to drive over the posted limit as long as you are driving safely. Say, for instance, you are driving 40 mph in a 35-mph zone, you are “presumed” to be speeding. But if it is 7 a.m. on a clear, dry morning with no other cars on a wide, straight road, and you can convince the judge that you were driving safely given those conditions, you could well be acquitted. That's a sizable "if," however.

The basic speed law theory states that you can be charged with speeding by violating the “basic” speed law, even if you were driving below the posted speed limit. An officer must simply decide that you were going faster than you should have been, considering the driving conditions at the time.

To find out which system your state or locality follows, start by looking up your state’s law and consult FindLaw's When Speeding Isn't Speeding article.