The statistic was alarming enough on its own: The number of cyclists killed by motor vehicles on New York City streets in 2016 had matched 2015’s total just eight months into the year.

But beneath that news was another concern. Eight out of 15 of the deaths occurred in Brooklyn, which is considered to be one of the most bicycle-friendly boroughs and is home to the city’s largest number of bicycle commuters. Three of the deaths had occurred in the Bronx and two in Manhattan, while Queens and Staten Island had one apiece.

Cyclists interviewed around Brooklyn on Friday searched for answers as to why the borough had become the most dangerous for cyclists in the city. Many said that while Brooklyn had become more bicycle-friendly in recent years, as had the city at large, the statistics proved there was much room for improvement, particularly in an era in which one of Mayor Bill de Blasio’s main efforts, Vision Zero, aims to eliminate traffic deaths entirely.

Alex Picca, 38, the owner of a bike shop with locations in Bedford-Stuyvesant, Brooklyn, and in Ridgewood, Queens, said that infrastructure, particularly bike lanes, still lagged in many parts of Brooklyn. Even where there were bike lanes, the gaps between them in many areas left some cyclists vulnerable for portions of their commutes. “Over the past year or two years, I haven’t really noticed a meaningful difference,” Mr. Picca said.