They put the brakes on bikes.

Progress is stalled on a Prospect Park West bike lane after Borough President Marty Markowitz asked city Transportation Commissioner Janette Sadik-Khan to kill the project.

"I've repeated to you on a number of occasions that anyone using their bike has a greater ability to do so without using Prospect Park West," wrote Markowitz to Sadik-Khan in a letter last October. "As Borough President of Brooklyn, I urge you to shelve this project indefinitely; and I await your reply."

Sadik-Khan never wrote back to Markowitz but the agency also never went forward with its plan.

"We don't know if the bike lane's in a state of hibernation or active study," said Community Board 6 District Manager Craig Hammerman, whose board voted to conditionally approve the Park Slope project in May. "We hope it's active study since it's an important traffic issue for the community."

The DOT plan would have added a two-way bike lane to the busy one-way road and reduced the number of lanes for cars from three to two.

Road work on the project was supposed to begin last September, but never started. DOT officials refused to say why - or when or if the work would commence.

In his letter to Sadik-Kahn, Markowitz argued the bike lane would increase congestion and reduce available parking. He also suggested that bikers use the Prospect Park bike path instead of the street to travel along the West side of the park.

His opinions weren't shared by many bikers and advocates, who said that DOT needs to stick to its guns and build the lane.

"Prospect Park and Park Slope are some of busiest bike destinations in New York," said Transportation Alternatives spokesman Wiley Norvell. "We want DOT to do what they said they'd do, and build the bike lane."

Park Slope residents and commuters said that the street is already plagued by traffic, speeding and lousy parking, and a bike lane couldn't make matters much worse.

"Right now it's a problem for everyone," said Elaine Roque, 36, an arts administrator from Crown Heights who bikes on Prospect Park West several times a week while doing errands. "And it's just going to get worse in the summer."