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A bike messenger was fatally hit by a truck while riding in morning traffic in Manhattan. Three days later, another cyclist was struck and killed by a car in Brooklyn.

And four days after that — less than four miles from the last crash — still another cyclist died after being struck by a cement truck.

The shocking spate of three deaths in a little over a week has drawn anguished cries from cyclists and transportation advocates and has undercut Mayor Bill de Blasio’s signature transportation policy to make the streets safer.

“New Yorkers on bikes are being killed at an alarming rate,” said Marco Conner, the interim co-executive director of Transportation Alternatives, an advocacy group.