Three people were killed and two were injured on Sunday in separate collisions across New York City in which pedestrians and a cyclist were hit by motorists who fled the scene, the police said. No arrests had been made, and each of the five episodes remained under investigation.

The crashes occurred after the number of fatal traffic collisions involving pedestrians in the city decreased in 2015 for the second year in a row, and after Mayor Bill de Blasio announced in 2014 an ambitious effort called Vision Zero to eliminate traffic deaths in New York by 2024.

At least 19 pedestrians have been killed in 2016, according to police statistics. At least three cyclists have been fatally injured, according to data from the city, and more than 900 pedestrians have been injured in collisions this year.

Those figures were elevated on Sunday by the string of collisions that started in the Bronx, just before 1:30 a.m., the police said.