Jamie Slater, 33, offered to excuse driving offences if the women agreed to meet up with him or give him their mobile phone numbers, Cardiff Crown Court heard.
He was convicted of misconduct while in public office.
The South Wales Police constable also used the force's database to retrieve personal details about his victims.
One woman was driving with only a provisional licence when Slater pulled her over, the court was told.
Peter Davies, prosecuting, said: "Mr Slater told her he would have to retain and impound the motor car she was driving.
"This caused her to be upset and she began crying. It was at that point Jamie Slater told her if she would give to him her mobile number he would not cause the car to be retained. She agreed to do so."
The court heard they began a consensual affair and on one occasion the pair met for sex while Slater was on duty and he received an emergency call on the police radio.
The police officer, of Port Talbot, South Wales, became involved in a high speed chase while the woman was hiding in the car, the court was told.
When her husband found out about the affair Mr Slater retrieved his details from the police database and sent him taunting messages, Mr Davies said.
One victim was pulled over when she drove through a red light and gave Slater her phone number because she was scared of the consequences of refusing, the court was told.
He later sent her graphic text messages.
Mr Davies said: "She was left scared and upset and said she will never get into a police vehicle again, having lost faith in the police force."
The barrister said all Mr Slater's victims felt powerless to do anything because he was a police officer in uniform.
Sentencing Slater, Mr Justice Lloyd Jones said he acted in "a particularly predatory manner."
He added: "These offences were deeply stressful to the victims.
"They felt powerless because you were a police officer.
"Your activities have caused immense damage to the public confidence in the police."
Mr Davies said Slater sent goading text messages to the husband of one woman after getting his number from the police database.
He said: "He began sending texts taunting him saying: "I'm f****** your wife...."
On another occasion, Slater pulled over a woman and told her he would impound her car for driving without insurance.
He said if she agreed to meet up with him he would see she got her car back without pay for the cost of the recovery.
The woman later told police: "It was a complete abuse of trust by someone in authority," the court heard.
Mr Davies said Slater sent her text messages asking her to wear stockings, saying he was aroused.
He later sent her messages telling her where she had been that day and what she was wearing. He also sent her a photograph of her driving her new car.
The barrister said: "She felt she was effectively being stalked. He would pull up in a patrol car outside her place of work and remain there for 20 minutes."
He later sent her a message saying: "I hope you burn in hell with your husband."
He sent another woman, who he pulled over for driving through a red light, messages saying: "Will you have sex with me today?"
The court also heard Slater pulled over a 19-year-old girl who was speeding on the M4 motorway and told her she could lose her licence if she was prosecuted.
He said he would let her off and asked for her mobile number.
The court heard he took her for drives in his patrol car and tried to kiss her and touch her leg.
Another of his victims was a pregnant woman Slater had never met.
He sent her a message saying: "Fancy meeting up for some sexy fun?"
The woman declined but Slater persisted. She eventually agreed to a meeting so she could find out who had been contacting her, the court heard.
When she arrived at the meeting place a police car pulled over and an officer asked her for directions.
The court heard that Slater was driving the car.
He later text her saying: "Did you used to be a working girl? How much do you charge for a f***? I want to f*** you. Will you send me a pic?"
Mr Davies said: "One day she received 35 texts with explicit requests for sex using vulgar tones."
Slater also met up with prostitutes while on duty. He contacted one asking if she wanted to join a business he was setting up selling sexual services. He later paid her for sex.
He met another prostitute, who he used to visit frequently as client and tried to have sex with her. When she refused because he had no money he later sent her an obscene text message.
Tom Crowther, mitigating, said Slater, who used to be a chartered surveyor, had always wanted to be a police officer.
He said: "It is perhaps a truism that wanting something is more compelling and satisfying than achieving it."
He told the court that Slater, who is married with two children, suffered from depression and had financial difficulties prompting him to set up a driving school to make extra money.
Mr Crowther added: "Underneath the uniform was a very insecure and unhappy man."
He said it was clear Slater would never work in the police force again and told the judge: "The opportunity to offend came from a position of authority.
"It is plain he will never again hold a position of authority."
Tom Davies, Independent Police Complaints Commissioner for Wales, said Slater was dismissed from South Wales Police in December.
He said: "Slater was a disgrace to all who work for the police service and abused the position of trust a serving police officer is given."
He added: "Slater was a rotten apple and acted alone.
"The public can be reassured that cases such as this are very rare, but where officers act in a criminal way they will be brought to account by the IPCC and the police service."
