In some of these cities it’s more about traffic cameras than about speed traps. They’re more likely to catch people who go through red lights or fail to stop at stop signs than those who are exceeding the speed limit.
A motorist was unknowingly caught in an automated speed trap that measured his speed using radar and photographed his car. He later received in the mail a ticket for $40 and a photo of his car. Instead of payment, he sent the police department a photograph of $40. Several days later, he received a letter from the police that contained another picture...of handcuffs. The motorist promptly sent the money for the fine. :)