Safer Intersections for All

Throughout the city, little “islands” are popping up between bicycle lanes and other traffic lanes in order to make this city safer for pedestrians, motorists and cyclists alike.

“When DOT presented plans for a protected bike lane on Sixth Avenue, one point of contention was the design of intersections. How many intersections will get split-phase signals, where cyclists and pedestrians crossing the street get a separate signal phase than turning drivers? And how many will get “mixing zones,” where pedestrians and cyclists negotiate the same space as turning drivers simultaneously? DOT tends to opt for split-phase signals only at major intersections, like where Sixth Avenue crosses 14th Street and 23rd Street. At other cross streets with turning conflicts, the mixing zone is the go-to treatment. Manhattan Community Board 4 wants to change that, asking DOT to include more intersections with dedicated crossing time for pedestrians and cyclists in the Sixth Avenue project.”

So what is a split phase signal? A split phase signal is essentially a double traffic light. One for motorists in the main part of the street and the other is for bicycles and pedestrians who are in the designated lanes. It has been implemented in order to give each person a chance to cross without the danger of getting hurt by other motorists/vehicles.

A 2014 DOT report [PDF] analyzed three years of before and after crash data from Manhattan’s protected bike lanes. The last section of the report shows the change in total crashes with injuries on 12 protected bike lane projects – six with primarily split-phase treatments (segments of Eighth Avenue and Ninth Avenue below 23rd Street, and two unconnected segments of Broadway in Midtown), and six with primarily mixing zones (segments of First Avenue, Second Avenue, Columbus Avenue, Broadway, and Eighth Avenue above 23rd Street). We don’t have access to the raw numbers DOT worked with, but the aggregate data strongly suggests that split phase treatments are significantly safer. On average, crashes with injuries declined 30 percent on the six “split-phase” redesigns and 13 percent on the six “mixing zone” redesigns. On eight protected bike lane segments, DOT also analyzed cyclist injury risk, a measure that, roughly speaking, divides the number of cyclists killed or severely injured on a given street segment by the number of cyclists counted on that street. Two of those segments, on Ninth Avenue and Broadway, were primarily split-phase projects while the others were primarily mixing zone projects.

So what is considered to be safer? And what is considered more cost effective? Unfortunately the answers to both these questions may not match up, meaning that a split phase signal may be safer but a mixing zone may be more cost effective.

Overall, these two options could only benefit pedestrians and cyclists, who are more vulnerable than motorists when travelling the streets on New York City.



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