You’re right that when the prosecutor asked the Defendant about the speed he was going and he admitted that he was going above the speed limit, it was not proper testimony. However, because it was a admission of a party to the action it could be used against the defendant anyway.
In general, a statement of a witness must be sworn and given at trial. If it isn’t it is hearsay and not admissable unless an exception applies. One of the exceptions is an admission of a party to the action. If a party to litigation (in this case, the Defednant) makes a statement in which he admits to what is alleged against him, his opponent (in this case the prosecution) can introduce sworn the testimony of someone who heard the party make the admission. (In other words, anything you say actually can be used against you in a court of law, because of this hearsay exception.)
Now if this were something more formal than traffic court, the judge might not simply find the Defendant guilty, but rather might put the police officer or some other witness on the stand to repeat in sworn testimony what everyone just heard. In traffic court, it seems that they just dispensed with this bit of unnecessary formality.
In other words, anything you say that may be an admission of guilt or liability can be used against you. But, because of your Fifth Amendment rights, you don’t have to provide any testimony or admissions. When you are acting as your own lawyer you should be careful about not making any damaging statements.
Rick suggested:
I would make a similar point, but do it slightly differently, because if the prosecutor answers Rick’s question “yes,” you will have to then point out that you can delcine to testify under the Fifth Amendment, and perhaps look to the jury like you are hiding something.
I would say: “I’m sure that the prosecutor knows that I am not required to testify here, but rather the prosecution must prove its case beyond a reasonable doubt.” That should remind everyone that this is a criminal case, that the Defendant does not have to testify, that the prosecution has to prove its case, and that the proof must be beyone a reasonable doubt. It will also make the prosecutor look a little overreaching.
Good Luck.