This sounds like it may be a question of fact. Those are generally decided by a Judge at a Bench Trial or your Peers at a Jury Trial. What offense was charged on the ticket?
As is noted above, this is really a fact issue that can be challenged at trial. The Dallas Municipal Courts are backlogged and if you challenge the ticket you have a chance that it will be dismissed. If not dismissed, you can go to trial and try to beat the cited offense. While an attorney is not always necessary, it can help to guide through the process.
Good luck, and feel free to contact me to discuss your options in Dallas Municipal Court.