Here's a hypothetical: Your license is currently suspended pursuant to one of the penalties for driving under suspension in Pennsylvania. You have been getting rides to work or taking public transportation. Your wife or husband has been patient as you wait to restore your driving privileges. Then, you are sitting at home and your wife or husband goes into cardiac arrest. Or, while you are getting a ride, the person driving you has a serious seizure. While you are driving the person to the hospital, you get pulled over for going to fast. You explain to the police officer that you are driving someone to the hospital. But, the officer sees your Pennsylvania driving license is suspended and you get charged under 1543(a) or 1543(b) for driving under suspension.
You do have a defense. In Commonwealth v. Manera, the court ruled that a person can use a "justification defense" because there was no clear legislative intent to the contrary. What this means is that an individual can "justify" why it was important for them to break the law.
The Bucks County Judge hearing the summary trial or appeal will have to make a determination whether your reasons for driving were valid.