Patrols on the Midtown Greenway are being beefed up and extra precautions are being urged after a string of three late-night robberies of cyclists on the Midtown Greenway that represent the most concentrated attacks there since early 2012.

Police said that cyclists were robbed at or shortly after 11 p.m. on the greenway on Saturday, Sunday and Tuesday. All of the attacks took place in the 12 blocks between Chicago and Cedar avenues, and involved two or three attackers.

In two of the three cases, police said, assailants knocked the victims off their bicycles. A stun gun was used in one assault, and a revolver and homemade knife were used in another. The robbers took backpacks, cellphones and money.

The Midtown Greenway Coalition, which runs a trail watch of unarmed volunteers, said it is considering extending the hours of that patrol. The coalition previously has advised late-night bikers to consider joining another cyclist when riding late at night.

Soren Jensen, the coalition’s executive director, said the attackers appear to be using the 18th Avenue ramp to the greenway for access. He said that police have indicated that they’ll step up car and bike patrols, and the coalition is looking into hiring off-duty police.

He advised bicyclists who spot groups of people under bridges not to try and power through them but to turn around and call 911.

“We are very concerned,” Jensen said, but added that the concentrated location and timing might aid in apprehension. “We’re hoping that police can catch these guys and put a stop to it,” he said. Police asked anyone with information about the attacks to call Sgt. Ker Yang at 612-673-3856.

The most concentrated previous series of attacks posted on the coalition’s safety log was four during a 75-day period between November 2011 and February 2012.

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