State Sen. Marty Golden impersonated a police officer from the passenger seat of a Cadillac as he attempted to bypass Brooklyn traffic — and his driver went on to run a red light when Golden was confronted about it, according to a cyclist who claims to have caught the senator in the act.

The cyclist, Brian Howald, a member of Brooklyn’s Community Board 2, said he was riding down Third Avenue Monday night in South Slope when Golden, a Republican, shouted at him from his window.

Howald, who posted about the altercation on Twitter, was heading south in the bike lane at around 14th Street. Golden’s driver had pulled into the bicycle-only lane to try to drive around the traffic that had backed up on Third Avenue, Howald said.

The cyclist refused to let the vehicle pass and that’s when Golden allegedly rolled down his front-seat window and yelled that he was a police officer. The senator waved what appeared to be a parking placard out his window as if it were proof, Howald said.

“I told him that he was illegally in the bike lane,” Howald said. “That’s when the passenger told me that he was a police officer, he demanded me to move over and he waved a placard out the window.”

Fearing that he would be ticketed or arrested, Howald pulled over and Golden’s driver rolled by, according to the cyclist. The Brooklyn Heights resident said he didn’t recognize Golden, but realized that his placard didn’t match those of the police department. Howald then attempted to approach the car and ask Golden what precinct he was from.

“A------,” Golden allegedly responded.

Golden is a former NYPD officer who retired in 1983 on disability after being injured on the job.

Howald then took out his phone and attempted to film Golden to alert police. Golden’s car was stopped in traffic, but his driver moved into the northbound lanes of Third Avenue and traveled south against traffic to slip away, the cyclist said.

Howald managed to catch up to Golden’s car again, after the senator’s vehicle turned left onto 19th Street from Third Avenue. The software engineer again pressed Golden for his precinct and asked the senator who he was.

“Wouldn’t you like to know?” Golden said, according to Howald. As soon as passing traffic cleared, Golden’s driver got away by driving through a red light at the intersection, the cyclist said.

But the two met once more shortly at the intersection of Fourth Avenue and 34th Street as Howald was pedaling to a Community Board 7 meeting. He tried to snap photos of Golden, who appeared to duck behind the visor of his car to shield his face, Howald said.

During an appearance on NY1 Tuesday night, Golden characterized the incident as a case of “cyclist road rage.” He insisted that Howald’s recounting was false and denied that he impersonated a police officer.

“My placard is in my window. If he wants to presume that we were police officers, or whatever he wanted to presume, that was in his head. We didn’t do anything to lead that on. And he is the one that said we used our placard illegally. That’s not true.”

In September 2005, Golden fatally struck a 74-year-old woman with his car, but was not charged in the crash because investigators found the woman to be crossing against the traffic light.

While it is not clear if Golden owns the car he was driven in, the license plate number associated with the vehicle has racked up more than 30 parking tickets since August 2013 — including 10 camera violations for speeding in a school zone.

Seven of those speeding tickets took place in Golden’s South Brooklyn district. Golden has been one of the most vocal critics of the school zone speed camera program and has fought legislative attempts to expand the city’s use of the cameras.

“It’s certainly disheartening, but I’m not terribly surprised. I think we’ve come to expect that many people in this city will use their placards or their positions of authority to evade traffic laws,” Howald said. “But I was taken aback to learn that the senator would impersonate a police officer and that he has obstructed efforts to make streets safer outside of schools — while the car in which he was driven has so many violations for speeding in school zones.”