Three people were killed and four others were injured after being struck by vehicles over the weekend, police said.No summons were issued and no arrests were made in the unrelated accidents as of last night.A 27-year-old woman was in critical condition after being struck at about 3 a.m. yesterday by a 2006 BMW in front of 3168 East Tremont Ave. in the Bronx. Another victim, an unidentified 23-year-old woman, was also injured in that crash and was listed in stable condition last night at Jacobi Hospital.In Manhattan, Ariela Koenigsberg, 72, was struck by a 2007 Ford at East 84th Street and Third Avenue at about 1 p.m. yesterday. Koenigsberg, of Bayside, was later pronounced dead.A 47-year-old man was struck and killed at about 2 a.m. yesterday by a black Lincoln Town Car that fled the scene near West 31st and Surf Avenue in Brooklyn.Also in Brooklyn, three pedestrians, including a 68-year-old man, were struck by a tan 1997 Dodge Caravan travelling eastbound on Neptune Avenue near West 24th Street at about 6 p.m. Saturday, police said. The unidentified elderly man was later pronounced dead at Coney Island Hospital. Two additional victims, a 46-year-old man and a 67-year-old woman, were taken to Lutheran Hospital in serious but stable condition. The driver refused medical attention at the scene.Three people were killed by vehicles last weekend and transit advocates called on the mayor to institute changes they claim will reduce pedestrian injuries and fatalities.City transportation officials acknowledged last week that "more needs to be done" regarding pedestrian safety despite figures that show 2004 and 2005 were the two lowest years in term of fatalities since 1910, with 156 deaths each year. Last year, 163 pedestrians were killed.