As a recent convert to New York City bike riding, I’m pretty timid about traffic. I don’t run red lights, I only ride in designated bike lanes, and I stay out of the way of other bikers who are in a hurry. About half my ride to work from Brooklyn to Columbus Circle is spent on regular bike lanes alongside cars, buses and taxis—stressful. I breathe a sigh of relief when I finally cross over to the west side and head north on the greenway. Completely separated from traffic, it is planted with dune roses and other beautiful vegetation, and it’s a blissful and (I thought) totally safe ride. As I cruised along this week, I was shocked to notice not one but two ghost bikes chained along the greenway: one, in the West Village in memory of 22-year-old Eric Ng, and other in honor of Dr. Carl Henry Nacht, 56, up near 38th Street. They were potent reminders of fate and the fragility of existence.