BOSTON (AP) β€” People keep tossing traffic cones in the Charles River. The Massachusetts Department of Transportation keeps retrieving them.

Surveillance video released Friday following a public records request by NBC Boston showed several people hoisting the orange cones and tossing them one by one off the Massachusetts Avenue Bridge.

Earlier this month, workers spent hours retrieving more than 100 cones from the ice on the river.

β€œIt is a little bit of a dicey operation whenever you have ice on a river. It can be dangerous,” MassDOT Highway Administrator Jonathan Gulliver told NBC Boston at the time.

The cones have been repeatedly removed from the bridge connecting Boston and Cambridge. They are part of a bicycle safety pilot program that launched in November.

MassDOT officials said it was unclear why people have tossed the cones off the bridge.