One of the tightest stretches of the Brooklyn-Queens Expressway is about to lose a lane.

Starting Monday morning, the city Department of Transportation will reduce the number of lanes in the triple-cantilever section of the BQE, from Atlantic Avenue to the Brooklyn Bridge in both directions, as part of long-planned repairs and updates to the crumbling highway.

Each direction of the expressway will go from three lanes to two lanes. The DOT said the lane reduction will help lighten the weight on the roadway and extend its lifespan. A report from an expert panel last year found that particular section needed to be repaired "immediately."

"The presence of many overweight trucks and faster-than-expected deterioration may cause sections of the road to become unsafe and incapable of carrying current traffic within five years," the report warned.

There’s also work to widen the lanes to reduce collisions from 10.5 feet to 12 feet and include a 9-foot shoulder that would alleviate traffic jams when accidents occur.

The DOT warned of “substantial delays” as a result of the lane reduction and asked motorists to consider public transportation instead.

“Trucks and essential vehicles should explore alternative routes, and prioritize the use of the Hugh L. Carey Tunnel and the New Jersey Turnpike,” the DOT said in a press release.

“During this necessary work on the BQE, we strongly encourage drivers to seek alternate routes and use public transportation. This lane remarking may be inconvenient for some, but it is essential to making the road safer immediately and for decades to come,” said DOT Commissioner Hank Gutman in the release.

The city said earlier this month it's hoping these measures will buy time for the next 20 years as DOT officials try to come up with a permanent solution to the problematic stretch, which is pocked with corroding rebar and deteriorated joints.

The lane redesign should result in only a 10-11% difference in additional traffic, the DOT has said.

To deter trucks that weigh more than 40 tons — and aren’t permitted on the BQE — from further damaging the roadway, the city hopes to install an automated ticketing system that will issue fines, rather than rely on the NYPD to enforce traffic regulations. That will require state approval.