How many people are allowed in a car with a driver under the age of 18?

I am a new driver, 16 and a half years, and I heard a rumor that the state of pennsylvania passed a law that stated there can only be one other person in a car with a driver under 18. I was wondering if this law was true. Most probably will not know, because it is said that the law will take a minimum of 90 days to take into effect. I know that it will be a secondary effense.