the free dictionary describes it as either,
Moving with speed.
OR,
The act or an instance of driving especially a motor vehicle faster than is allowed by law.
When you're describing something to which no legal speed limit applies, e.g. a formula one car, or a bullet, then it's obviously the first one. e.g. there is no meaning to 'faster than is allowed by law' for a bullet, F1 car, or train, so it's obviously the first one.
Now, the first one is
also valid for a car that is driving on the public road, but the mere fact that there's the possibility for it to mean the second one in this instance, steers the interepretation towards ambiguity at the very least. It's this ambiguity you really want to avoid.
Perhaps other words could accompany the word 'speeding' (and/or replace it) to steer the interpretation towards the first definition without the sentence losing the impact it was designed to have? I notice thefreedictionary uses 'adj' for the first one and 'n' for the second, I wonder if that element of language could be used to this effect?
HTH....