UPPER WEST SIDE — The writing of traffic tickets "came to a virtual standstill" on the crash-plagued Upper West Side as NYPD officers carried out a slowdown after the murders of Detectives Wenjian Liu and Rafael Ramos, officials said.

The lack of action caused the mother of 9-year-old Cooper Stock, killed by a cab as he crossed West 97th St., to accuse them of putting more lives at risk.

In the week following the Dec. 20 shootings, from Dec. 22 to 28, there was only one ticket written for a hazardous violation — which includes texting, failure-to-yield to a pedestrian, speeding and running a red light — compared to 136 tickets in the same period the previous year, 24th Precinct data shows.

There were only two tickets written for moving violations — which include parking in a bus lane or a crosswalk and double parking — compared to 120 in the same period last year, according to the data.

Liu and Ramos were shot in Bedford-Stuyvesant by Ismaaiyl Brinsley, 28, who had bragged on social media that he planned to kill police in response to events in Ferguson, Mo., and the death of Eric Garner on Staten Island.

In response, officers at the 24th Precinct "were doing reactive policing" rather than proactive policing, explained Capt. Timothy Malin, who's in charge of traffic safety for the area, which runs from West 86 to 110th streets, between Central Park and the Hudson River.

Officers responded to every 911 call and made arrests, but they were voicing their anger and frustration through not writing summonses, Malin acknowledged.

"They were upset," he said. "They were shaken."

Residents have demanded more police enforcement and attention paid to drivers who fail to yield to pedestrians after last year's string of deaths in the West 90s.

Cooper was killed last January when a cabdriver failed to yield as he and his dad crossed the street. The taxi driver was accused of failing to yield.

In July, a driver struck and killed an Upper West Side woman Jean Chambers, 61, who was walking in a crosswalk.

Dana Lerner, Cooper's mother, described the slowdown as "disheartening" and called for more education for officers so that they see this kind of police work as vital.

"I wonder if [the police officers] understand how important it is to write these tickets [and] if they understood that by doing so they could be saving a life," she told DNAinfo New York.

In response to the slowdown, Capt. Marlon Larin, the precinct's commanding officer, spoke to the precinct's roughly 112 officers in early January, Malin said, leading to a return of a normal level of ticket writing.

From Jan. 12 to 18, there were 133 hazardous violation tickets written by 24th Precinct officers compared to 127 in the same period last year, NYPD data shows. There were 154 moving violations issued, compared to 169 during the same period last year.

The slowdown does not appear to have affected the number of vehicle crashes in the 24th Precinct. In the week following the officers' deaths, there were 13 crashes, including one in which a pedestrian was injured and one in which a driver was injured. During the same period in 2013, there were 19 crashes, with four pedestrians and a cyclist injured.

Tickets for double parking are still at record lows, a fact that troubles Malin because the violation is dangerous for cyclists, pedestrians and drivers who have to navigate around the cars, he said.

From Dec. 22 to 28, only three parking violations were handed out in the precinct, data shows. While 303 were handed out last week, the figure represents a nearly 38 percent dip compared to the same week last year, when 487 parking violations were handed out, data shows.

"We're not at 100 percent," Malin said, adding that he feels positive about the direction the numbers are headed.

In early January, Commissioner Bill Bratton admitted that a slowdown was occurring across the NYPD, characterizing the police work that stopped as "discretionary."

The NYPD is investigating the roots of the slowdown, he said at the time.