Repairs have finally started on the busted-up Ocean Parkway bike lane, a key route that connects Brooklyn’s Prospect Park to Coney Island that has been dangerously cracked for years — but conditions are still dangerous because the Parks Department has not created the necessary detour.

The Parks Department’s contractor closed off the northernmost block of the project in recent weeks to fix the cracked 1894 path between avenues R and X — more than four years after it got funding and following repeated setbacks that officials blamed on the pandemic and its contractor.

The agency initially has also neglected to set up a legally required safe detour for cyclists on the closed section of the vital 5.5-mile link, which runs through an area with no other north-south protected bike paths.

A sign at the fenced-off area just says “SIDEWALK CLOSED USE OTHER SIDE,” making it unclear whether bikers should use the pedestrian-only lane on the east side of the parkway, the highway-like roads, the service roads, or the sidewalks to get around the construction zone.

Cyclists are already using the service road in both directions as a replacement for the two-way greenway, even though its a one-way street, said one cycling advocate who visited the scene on Monday.

“It’s another classic Parks Department greenway moment,” said Jon Orcutt, the advocacy director at Bike New York.

The Parks Department and the Department of Transportation plan to post signs for a detailed detour by the end of the week, according to Parks spokesperson Chris Clark, who said the current signage was only temporary.

The sign also had a wrong completion date set for this fall, but the $2.6-million, seven-block project will continue through March 2024, said Clark, as per the agency’s online project tracker.

Rather than closing down the whole stretch, the project will renovate the paths in two-block increments, Clark said.

The agency has a history of failing to provide safe alternatives for the many cyclists that rely on its greenway infrastructure.

Last year officials closed off 1.4 miles of the Hudson River Greenway uptown — the nation’s busiest greenway — and directed riders onto dangerous neighborhood streets for months, rejecting calls from locals to take a lane of the Henry Hudson Parkway.

There are also plenty of spots outside of the scope of the current project that are in dire need of some fixes, Streetsblog found in December.

The once-glorious 19th-century path — the city’s first protected bike lane — has been deteriorating since at least 2010, but the Parks Department only committed to making the fixes when then-Borough President Eric Adams and former Council Member Mark Treyger put up the money in 2019.

Treyger, who was term-limited out of office last year, celebrated the project’s progress on social media.

Thank you @NYCParks ! Proud to have secured the resources to advance this much needed improvement for residents. Thank you @bikenewyork for your advocacy and support!

— Mark Treyger ? (@MarkTreyger718) May 1, 2023

Construction was supposed to start in 2021, but Parks pushed it back by a year due to the pause in city projects during the first year of the Covid-19 outbreak, and then again to 2023 because officials had to make sure the lowest-bidding contractor was paying fair wages, agency officials previously told Streetsblog.

Lawmakers have introduced legislation to shave 25 percent off the timeline of Parks’s notoriously slow capital projects. The Department of Transportation would be far better suited to handle repair of transportation infrastructure, said Orcutt, who used to work as a policy director for DOT under former Mayor Michael Bloomberg.

“They should be working on it based on function,” he said. “Instead of sending DOT, [Parks] go out to contract and it takes them five years.”