The movie, notable for its car chase, was produced and directed by Philip D'Antoni, who had also produced Bullitt (1968) and The French Connection (1971), two pictures which were also notable for their car chases.
None of the car chase was rehearsed, as the producers knew that if the police and authorities assisting the shoot, saw what was planned, they would never have given permission for it to proceed.
According to Dennis Farina in Episode Episode #3.1 (2004) of Dinner for Five (2001), this film was the most realistic in its depiction of cops. Farina was once a cop who worked in Chicago.