"Absolute" speed states set an upper limit, above which your speed is considered illegal. Drive one mile over the limit and you are a lawbreaker. But these states also have a way to ticket you when you are driving under the speed limit if the cop concludes your speed was unsafe. Called the "basic" speed law, it prohibits driving at an unsafe speed, even if that speed is below the posted limit.
"Presumed" speed limit states also have the same law, although it is usually written into the "presumed" law. Or put another way, since the posted speed limit is presumed to be safe only when road or traffic conditions are good, the presumption can be rebutted by the police officer and the safe speed can be much lower.
But technicalities aside, in all states, tickets for driving under the speed limit, but too fast to be safe, are often referred to as "driving too fast for conditions."
For example, driving exactly at the 65 mph posted limit on the freeway would be unsafe amidst slower and heavy traffic, in a dense fog, or in a driving rainstorm or blizzard.
In common sense terms, such unsafe driving is unlawful, regardless of higher speed limits. Police most often rely on the "basic" speed law after an accident. They reason that you were driving too fast, no matter how slow you were driving, because you were in an accident.
The difference between fighting one of these tickets and a speeding ticket for going over the speed limit is that here the prosecution has the burden of proving you were driving unsafely. (Again, that's because the posted speed limit is presumed to be safe.) This means the officer must testify that given the unusual road, weather, or traffic conditions, your below-the-limit speed was still unsafe. This can be tough to do unless you were involved in an accident, because the cop may be hard put to come up with enough evidence to rebut the presumption established by the posted limit. If you were in an accident, the officer will probably try to show that it was evidence you were driving at an unsafe speed, and if your speed had been lower, you would have avoided the accident.
However, you do not have to despair even if you were in an accident and are charged with violating the "basic" law for driving at an unsafe below-the-limit speed. The fact that you've had an accident is not absolute proof that you were driving unsafely. Accidents, after all, are not always caused by your violating the law. Often, they are caused when another driver screws up.
If the police officer argues that the accident itself is evidence that you were driving at an unsafe speed, even though you were not technically speeding, you must be prepared to challenge that assertion. Your best bets are normally to claim, and hope fully prove, that the accident could have occurred for a number of reasons. For example, it could have been:
Never plead guilty to a ticket issued to you following an accident. Seek the advice of an attorney. Even if you don't want to fight the ticket, you should enter a "nolo contendere" plea, which is a way of not fighting the charges. A guilty plea can be used against you if anyone involved in the accident sues you for damages. By contrast, if you fight a citation and lose, a guilty verdict might be used against you in a civil lawsuit arising from the accident.