Since there seems to be a lot of speculation about this, IANAL but from what I can gather, someone who kills someone with their car could be charged under any of these 3 statutes.
I think it's pretty ridiculous that the first one even exists.
http://law.onecle.com/pennsylvania/vehicles/00.037.014.000.html
75 Pa § 3714. Careless driving.
(a) General rule.--Any person who drives a vehicle in careless disregard for the safety of persons or property is guilty of careless driving, a summary offense.
(b) Unintentional death.--If the person who violates this section unintentionally causes the death of another person as a result of the violation, the person shall, upon conviction, be sentenced to pay a fine of $500.
(c) Serious bodily injury.--If the person who violates this section unintentionally causes the serious bodily injury of another person as a result of the violation, the person shall, upon conviction, be sentenced to pay a fine of $250.
(d) Definition.--As used in this section, "serious bodily injury" means any bodily injury which creates a substantial risk of death or which causes serious, permanent disfigurement or protracted loss or impairment of the function of any bodily member or organ.
http://law.onecle.com/pennsylvania/vehicles/00.037.032.000.html
75 Pa § 3732. Homicide by vehicle.
(a) Offense.--Any person who recklessly or with gross negligence causes the death of another person while engaged in the violation of any law of this Commonwealth or municipal ordinance applying to the operation or use of a vehicle or to the regulation of traffic except section 3802 (relating to driving under influence of alcohol or controlled substance) is guilty of homicide by vehicle, a felony of the third degree, when the violation is the cause of death.
http://law.onecle.com/pennsylvania/crimes-and-offenses/00.025.004.000.html
18 Pa § 2504. Involuntary manslaughter.
(a) General rule.--A person is guilty of involuntary manslaughter when as a direct result of the doing of an unlawful act in a reckless or grossly negligent manner, or the doing of a lawful act in a reckless or grossly negligent manner, he causes the death of another person.
(b) Grading.--Involuntary manslaughter is a misdemeanor of the first degree. Where the victim is under 12 years of age and is in the care, custody or control of the person who caused the death, involuntary manslaughter is a felony of the second degree.