Under Pennsylvania law, government entities are generally immune from liability, meaning that you can't sue the government in negligence cases. However, there are some limited exceptions, one of which applies to car, bus and pedestrian accidents with a government-owned car or transit vehicle.
In addition, because the government would be a party to the case, there are some specific requirements that accident victims must follow for these kinds of cases. First and most importantly, there is a mandatory 6 month notice requirement. An injured person must notify the correct government agency within 6 months of the date of the accident. Also, that notice is required to contain specific information.
Our recent article, In Pennsyvlania is the Government Liable for Car Accidents discusses these issues in more detail.