A 16-year-old girl was hospitalized earlier this week after she was struck by a van at 48th Street and Sixth Avenue in Sunset Park in Brooklyn. Earlier this month, a 9-year-old boy was fatally struck by an SUV driving on the sidewalk as he walked with his mother on Fort Greene's Clermont Avenue.

In response to the tragic accident in Fort Greene, and to years of unsafe driving in the neighborhood, residents and members of Make Brooklyn Safer, a group that promotes traffic and street safety, marched to the 88th Precinct on Tuesday. Pedestrian advocates held a similar rally on the steps of City Hall in August.

Under Mayor Michael Bloomberg, traffic deaths overall have declined. But some neighborhoods, especially in Brooklyn, are still unsafe.

According to the pedestrian and subway-rider advocacy group Transportation Alternatives, law-breaking drivers cause 60 percent of all city fatal crashes, with speeding being the most common cause. But even with excellent traffic-calming measures by the city's Department of Transportation, enforcement needs to be more aggressive.

Authorities appear to have responded to public outcry over the most recent Fort Greene accident. The motorist has been charged with criminally negligent homicide and assault.

We should demand that Mayor-elect Bill de Blasio work as hard as Bloomberg did to organize traffic patterns that are friendly to bicyclists and pedestrians.

The Department of Transportation has responded to concerns all over the city and established slow zones -- defined areas where the speed limit is cut from 30 mph to 20 mph, along with safety measures, such as signs, to change motorist behavior.

In Clinton Hill-Bedford-Stuyvesant, after many pedestrians were injured or killed in accidents, residents demanded a slow zone in an area navigated by many children (there are four schools as well as Head Starts, preschools and day care centers). Residents organized a letter-writing campaign, and the department created a slow zone last month.

The recent car accidents are awful, but this is a problem we can lessen with more slow zones and proper enforcement of traffic rules.

Mr. de Blasio, it's your turn.

Liza Featherstone lives and writes in Clinton Hill.