patrol car vs police car

patrol car and police car both are nouns.

Word	Noun	Adjective	Verb	Adverb
patrol car	Yes	No	No	No
police car	Yes	No	No	No

As nouns, patrol car and police car are synonyms defined as:

patrol car and police car: a car in which policemen cruise the streets; equipped with radiotelephonic communications to headquarters

Other synonyms of patrol car include cruiser, police cruiser, prowl car, squad car.

patrol car (noun)	police car (noun)
a car in which policemen cruise the streets; equipped with radiotelephonic communications to headquarters	a car in which policemen cruise the streets; equipped with radiotelephonic communications to headquarters