Just ahead of Memorial Day weekend, blocks and metal fencing have gone up at two points along the Prospect Park loop. The obstacles are intended to slow cyclists at major pedestrian crossings, but they form narrow chokepoints that may create more problems than they solve.

The cubes are located by the bandshell on the west side of the park and at the bottom of the hill on the southwest leg of the loop, according to reports on Reddit and Twitter.

What’s up with the concrete barriers in prospect park. At the band shell and at the lake. #prospectpark. #bikenyc pic.twitter.com/j26a8aJxhW

— Bicycle Habitat (@BicycleHabitat) May 25, 2018

The Prospect Park Alliance said DOT decided to install the pinch points. DOT said the agency installed the barriers “at the request of the Alliance for safety purposes.”

The bottom of the hill, where cyclists accumulate speed as they approach the crossing, has been the site of collisions that resulted in serious injuries.

Reducing the speed of downhill cyclists could prevent those types of crashes, but this design also introduces new risks. The big anchors are obstacles that appear suddenly, and may cause cyclist collisions or abrupt merging movements that jeopardize people on the loop.

The steep downhill on the park loop at this location poses a tough design problem. It would be reassuring if the city could point to a precedent for calming fast bike traffic on car-free streets shared with pedestrians, and duplicate it here. But the blocks and fencing look like standard materials for controlling cars that have been transposed to a car-free setting.

Correction: We originally reported that the blocks are concrete. DOT says they are plastic, not concrete. The post has been amended.