Simplify the following text for a Grade 9 native English-speaking person.
Original: The New York City Transit Police Department was a law enforcement agency in New York City that existed from 1953 ( with the creation of the New York City Transit Authority ) to 1995 .
Simplified: The New York City Transit Police Department , that was started in 1953 , was a transit police department for the New York City Subway and bus lines .