How much more over the speed limit must you go before a cop can impound your vehicle and take you off to jail?

I was looking at my local new station's website and they had all the arrest listed for the police department on Wednesday. I saw a couple of folks had been arrested for speeding! Ididn't know an arrest could be made on the spot for that, I thought it was only if an accident occurs from the speeding, but anything else could result in a license revocation and or taken, or jut a speeding ticket be issued!