From The Collaborative International Dictionary of English v.0.48 :
patrol wagon \patrol wagon\ n. An enclosed truck used by police to transport prisoners. Syn: paddy wagon, Black Maria. [WordNet 1.5]From WordNet (r) 3.0 (2006) :
patrol wagon n 1: van used by police to transport prisoners [syn: police van, police wagon, paddy wagon, patrol wagon, wagon, black Maria]